Doubt related with treeview control

Hi all

Im using treeview control.binding values from database with check box.
Nearly three childs are there for parent node.like
Parent1
child1
child2
child3
Parent2
child1
child2
child3
I can able to bind datas which is from 3 tables all working well.I want a facility when a parent node checks all its corresponding childs automatically get checked.If i click on parent 1 ,child 123 get checked .if i check child1,child2 and child3 get checked.if i check child 2 all child3 items get checked.How to do that?

Thanks in Advance
Amrutha