It would be highly convenient to be able to zoom in on a particular branch of the tree. Zooming in would temporarily make a branch the root level branch. This would be very helpful when you're working on a particular area of the tree and you don't want to be distracted by other non-relevant branches.
To see an example of how this has been implemented in another application, I would refer you to http://www.mylifeorganized.net
Zoom Function
Zoom Function
Brad S Konia