Take a look at this post in which Joseph Cooney discusses
virtualizing a Silverlight TreeView control.
For large hierarchies the TreeView in the Silverlight tool-kit suffers some performance problems, because the elements (once loaded and expanded, such that they could be seen by the user if they scrolled the scroll-bar) aren’t virtualized as aggressively as they could be. The for example the hierarchy shown below: If Child Node 4 is expanded, pushing Child Node 5 outside the limits of the view port of the TreeView then Node 5, as well as any other children of Node 4 that aren’t directly visible, _could_ be virtualized but currently aren’t by the Silverlight Treeview.
