[Solved] Treeview within a RadComboBox

[venm]

I have two RadComboBox & one of them has a treeview in it.  Same as cascading dropdowns When I select some item in my first radcombobox I need to load different items to my treeview (which is inside another radcombobox). But which event I can raise from the javascirpt for it ?
I tried combo.requestItems(node.get_text(),false);  I got error when I tried this.

Please help I am stuck.