It would be nice to know what state all of the files in a node/group/subtree are in. This would be helpful for large lists and when they are all collapsed - you could see if you are 'complete'.
Since I would *think* most of the time people would want *one* item unselected in a given tree (ie to keep it), you could highlight that with green.
Having all selected could be a problem (ie lose all copies), so highlight that red.
1) NONE selected (no background?)
2) ONE UNselected (green background - good to go)
3) ALL selected (red background - warning)
2.5) more than one selected = yellow?
I suppose you could use a 3-state checkbox for the top nodes, but this would be unclear what the selection value is for that file.