question about treeview

[Haiying]

Hi ,

I have a question about generating treeview.Here is my code:
Public Class Form1
Inherits System.Windows.Forms.Form

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e
As System.EventArgs) Handles Button1.Click
Dim aa As New TreeNode(1)
Dim bb As New TreeNode(2)
Dim cc As New TreeNode(3)
Dim dd As New TreeNode(4)
aa.Nodes.Add(bb)
aa.Nodes.Add(cc)
bb.Nodes.Add(dd)
cc.Nodes.Add(dd)
TreeView1.Nodes.Add(aa)

End Sub

End Class

the rusult is:
4
|
1-2
|
3-4
but i hope the result is :
1-2-4
|
3-4
How should I change my code?

Thanks a lot,

Haiying