Meh, seems to involve too much I would have to teach myself for a rather simple modification I is not really something I need, just something that would be nice to have...
I'll just describe how it's done in calibre in case "someone" feels like integrating it. ;-)
Assuming my database contains the collections
instead of showing all the collections, i would like to only see a "Series" and "Genre". If you click on "Series" it offers "Star Trek" and "Flavia". If you click on "Star Trek" it shows "(none)", "TNG", "VOY", and those then contain the books.
Personally I think a ":" of a ">" would make a better separator (see for instance the top of this page *g*) but the "." is what calibre uses...
I keep going on about calibre but this would of cause also be useful without calibre if you manage your collections in any other way.
And just to repeat, I'm talking about actual collections. You always come back to how files are stored in folders, but I don't use folders cause one book can be in multiple collections but only in one folder