In the below, the "buildon-'pv:extension'" results in my top tree (for videos in this case) to be based on the extension of the files.
So I can see my "avi" and "mp4" items seperately for example...
<container name='By Type' groupid='video/ByType' sortcriteria='+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'>
<container name='allname' createClass='object.item.videoItem.movie' class='object.container' />
<container buildon='pv:extension' sortcriteria='+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'>
<container name='playlistrecentlyadded' filteron='pv:modificationTime' sortcriteria='-pv:modificationTime' createClass='object.item.videoItem.movie' maxitems='100' upnp:originalTrackNumber='1' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1, pv:playlistRoot=Video' />
<container name='playlistlastviewed' filteron='pv:lastPlayedTime' sortcriteria='-pv:lastPlayedTime' createClass='object.item.videoItem.movie' maxitems='10' upnp:originalTrackNumber='2' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1, pv:playlistRoot=Video' />
<container name='Album' groupid='video/EDAlbumMain' upnp:originalTrackNumber='3' sortcriteria='upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'>
<container name='All Albums' groupid='EDAlbumsAll' upnp:originalTrackNumber='1' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:album' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
<container name='All Albums (ABC)' groupid='video/EDAlbumsAllABC' upnp:originalTrackNumber='2' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:album[3]' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:album' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
<container name='Year / Album' groupid='video/EDAlbumsByYear' upnp:originalTrackNumber='3' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='pv:year[1:4]' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:album' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
</container>
<container name='Genre' groupid='video/EDGenreMain' upnp:originalTrackNumber='4' sortcriteria='+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'>
<container name='All Genre' groupid='video/EDGenreAll' upnp:originalTrackNumber='1' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:genre' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
<container name='Genre / Recently Added' groupid='video/EDGenreRecentlyAdded' upnp:originalTrackNumber='2' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:genre' createClass='object.item.videoItem.movie' class='object.container'>
<container name='playlistrecentlyadded' filteron='pv:modificationTime' sortcriteria='-pv:modificationTime' createClass='object.item.videoItem.movie' maxitems='25' upnp:originalTrackNumber='1' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1, pv:playlistRoot=Video' />
</container>
</container>
<container name='Genre / Year' groupid='video/EDYearOfGenre' upnp:originalTrackNumber='3' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:genre' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='pv:year[1:4]' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
<container name='Year / Genre' groupid='video/EDGenreByYear' upnp:originalTrackNumber='4' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='pv:year[1:4]' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:genre' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
</container>
<container name='Star Rating' groupid='video/EDRating' upnp:originalTrackNumber='5' sortcriteria='upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'>
<container name='Rating / Album' groupid='video/EDRatingAlbum' upnp:originalTrackNumber='1' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='pv:rating' sortcriteria='-pv:rating' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:album' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
<container name='Rating / Genre' groupid='video/EDRatingGenre' upnp:originalTrackNumber='2' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='pv:rating' sortcriteria='-pv:rating' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:genre' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
<container name='Rating / Year' groupid='video/EDRatingYear' upnp:originalTrackNumber='3' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='pv:rating' sortcriteria='-pv:rating' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='pv:year[1:4]' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
</container>
</container>
</container>
<container name='Overall' groupid='video/Overall' createClass='object.item.videoItem.movie' class='object.container'>
<container name='playlistrecentlyadded' filteron='pv:modificationTime' sortcriteria='-pv:modificationTime' createClass='object.item.videoItem.movie' maxitems='100' upnp:originalTrackNumber='1' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1, pv:playlistRoot=Video' />
<container name='All Albums (ABC)' groupid='video/EDAlbumsAllABC' upnp:originalTrackNumber='2' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:album[3]' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:album' albumart='1' sortcriteria='+upnp:album,+upnp:originalTrackNumber' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
<container name='Year / Album' groupid='video/EDOverallAlbumsByYear' upnp:originalTrackNumber='3' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='pv:year[1:4]' createClass='object.item.videoItem.movie' class='object.container'>
<container buildon='upnp:album' albumart='1' createClass='object.item.videoItem.movie' class='object.container'/>
</container>
</container>
<container name='playlistlastviewed' filteron='pv:lastPlayedTime' sortcriteria='-pv:lastPlayedTime' createClass='object.item.videoItem.movie' maxitems='25' upnp:originalTrackNumber='4' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1, pv:playlistRoot=Video' />
</container>
<container name='playlists' id='video/playlists' class='object.container' createClass='object.item.videoItem.movie,object.item.videoItem.online.movie' sortcriteria='+upnp:originalTrackNumber,+dc:title' restricted='0' flags='pv:playlistRoot=Video' >
<container name='playlistrecentlyadded' filteron='pv:modificationTime' sortcriteria='-pv:modificationTime' createClass='object.item.videoItem.movie' maxitems='500' upnp:originalTrackNumber='3' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1' />
<container name='playlistmostviewed' filteron='pv:playcount' sortcriteria='-pv:playcount' createClass='object.item.videoItem.movie' maxitems='500' upnp:originalTrackNumber='1' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1' />
<container name='playlistlastviewed' filteron='pv:lastPlayedTime' sortcriteria='-pv:lastPlayedTime' createClass='object.item.videoItem.movie' maxitems='500' upnp:originalTrackNumber='2' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1' />
<container name='playlisthighlyrated' filteron='pv:highrated' sortcriteria='-pv:rating' createClass='object.item.videoItem.movie' maxitems='500' upnp:originalTrackNumber='4' restricted='1' class='object.container.playlistContainer' flags='pv:smartplaylist=1' />
<container buildon='upnp:playlist' sortcriteria='+upnp:originalTrackNumber' createClass='object.item.videoItem.movie,object.item.videoItem.online.movie' upnp:originalTrackNumber='5' class='object.container.playlistContainer' />
</container>
<container name='classifiedvideos' id='video/classified' class='object.container' createClass='object.item.videoItem.classified.movie'/>
<container buildon='pv:onlineServiceName' groupid='video/onlineservices' createClass='object.item.videoItem.online.movie' class='object.container'>
<container buildon='pv:onlineServiceTitle' createClass='object.item.videoItem.online.movie' class='object.container'/>
</container>
</container>