How to add the last node in a tree view?C#Error while adding last node what could be the reason?

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.NET1.1

.NET2.0

C#2.0

.NET3.0

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Am facing one issue, I have one tree view.
Inside that i have 3 child nodes.

problem here is, data coming properly but the expansion\collapse symbol of last node is not coming (showing red into mark)
also am unable to click and collapse that (showing error 'undefined data').
If i add a new child node to my last node then it will show the symbol but the newly added child node will note work (same problem).
So some problems with the last node.

Here am adding last node as child node instead of that can i add it as content(like text,label..).

What is the problem with last node?
How to add this last node?

Any solution?