I don't if this kind of thing exists yet but i come up with an idea of a new tree expandable widget.

This comes from the fact that when exploring a tree, you can get lost easily when diving much into tree element.
To find you way back, you have to scroll up very much.

So my idea would be to delete the scroll bar and keep any time where you are located.

Here is a mockup of what it could look like on dolphin (look at the folder tree) :



When descending the tree, the tree view acts as always.
But each time the tree height would need to be increased, the content of the top tree items are hidden except for the parents item of the current selected item.

When selecting an item that has been reduced, its content appears again and the past selected items are still expanded and visible.

We could imagine some kind of "magic scroll : the more i scroll up the more the content of the parents item are displayed.

I don't think i made my point yet.
I know it seems confused, that's normal, because my mind is not yet perfectly clear.

But if i could have the suggest of an usabilty guru.