General :: Link Parent / Child Node To A Control On Main Form In Treeview

I downloaded a sample treeview application I have modified most of its to suit my need, except one thing. I want link parent/child node the main form to the main form through a subform on the CategoryID.

The following is the original code where when a child not is clicked only pops up a "linked" msgbox. I need to modify the part of the code on the Select Case "C" in red:

Code:
'----------------------------
Sub DisplayForm(i As Integer)
'----------------------------
' for this Treeview I do not want a double-click on a parent node
' to open the applicable Category form, but pressing the shift key
' should open the marriage form applicable to the parent node. Shift
' or double-click on a child node should open the applicable
' offence form.

Dim strKey As String
Dim strTag As String
Dim strFilter As String

[Code] ....