codice:
Private myMouse As MouseButtonConstants

Private Sub TreeView_MouseDown(Button As Integer, _
                               Shift As Integer, x As Single, y As Single)
    myMouse = Button
End Sub

Private Sub TreeView_NodeClick(ByVal Node As MSComctlLib.Node)
    If myMouse = 2 Then  'vbRightButton
        MsgBox "cliccato"
    End If
End Sub