TreeView - validating values - BeforeEvent ?

Question

I have a treeView C#.

I have the following items

A
B
->B.1
->B.2
C
D

user selects B. Now if the user selects C or any other node I need to some check before leaving the selectiob B. Say i need to call a function and that return a true or a false. if it return a true then the selection can change but if its false the treenode B should still be selected. How can i acheive this?

Say the current selection was B and now user clicks C If i handle BeforeSelect event, the node string that is recd as parameter is C not B. I need to check if its B and then call the appropriate function

Am i handling the correct event