it may be a good idea to allow automatic scrolling like windows explorer, where dragging an object abovethe top or under the bottom of the visible part of a tree will trigger scrolling as long as the cursor does not come back in the tree window.
it may help, that using scrollto may work. the only small flaw is with this method, the dragged item is initialized in onbeingdrag amd the same variable will be saved over and over as long as its out of the window. the flaw is whenever the cursor enter the window again, onbeingdrag gets called again, thus reinitializing the item again.
This can be seen when trying to drag an item from the top to all the way to the bottom and enter the window and go to the top. whats going to happen is after re etnering the item will jump straight to the top.