>In addition to what Jamie and Jordan advise, You could just populate the >root nodes, and wait to add the children when the root is expanded

I tried that also, but there is 3500 root nodes and initialization of control is slow (2-3 min with Pentium II on client side).

I can simulate treeview behavior with grid but I don't like solution like that.

Infragistic control is too expensive for me. Is there some free control for specific task?