* it only contains "real" items, not nodes
* For example, if you open a directory, you will have
*\verbatim
- * Category tree: Onevelel tree:
+ * Category tree: Onelevel tree:
* Playlist Playlist
* - Dir - item1
* - Subdir - item2
* - input 1 -> name = foo 1 uri = ...
* - input 2 -> name = foo 2 uri = ...
*
- * Category tree Onlevel tree
+ * Category tree Onelevel tree
* - playlist (id 1) - playlist (id 3)
* - category 1 (id 2) - foo 2 (id 8 - input 2)
* - foo 2 (id 6 - input 2) - media library (id 4)