dim trv as winform.treeview=e.form.controls("tv1")
dim nd as winform.treenode=trv.selectednode
dim pnd as winform.treenode=trv.selectednode.ParentNode
dim ppnd as winform.treenode=trv.selectednode.ParentNode.ParentNode
Dim txt As WinForm.TextBox = e.Form.Controls("TB1")
dim dr as datarow
Dim Value As Integer=trv.selectednode.Level
Select Case Value
    Case 0
       dr=datatables("jg").find("sheng = \'" & txt.value & "\'")
       if dr is nothing then
           dr=datatables("jg").addnew()
           dr("sheng") = txt.value
           trv.nodes.add(txt.value,txt.value)
       end if
   Case 1
       if nd is nothing then
           return
       end if
       dr=datatables("jg").find("xian= \'" & nd.text & "\' and xian= \'" & txt.value & "\'")
       if dr is nothing then
           dr=datatables("jg").addnew()
           dr("sheng")=pnd.text
           dr("xian")=txt.value
           nd.nodes.add(txt.value,txt.value)
       end if
    case 2
     if nd is nothing then
           return
       end if
       dr=datatables("jg").find("xiang= \'" & nd.text & "\' and xiang= \'" & txt.value & "\'")
       if dr is nothing then
           dr=datatables("jg").addnew()
           dr("sheng")=ppnd.text
           dr("xian")=pnd.text
           dr("xiang")=txt.value
           nd.nodes.add(txt.value,txt.value)
       end if
End Select




上述代码如果不删除"dim ppnd as winform.treenode=trv.selectednode.ParentNode.ParentNode"代码,则不同增加省份,如果删除就可以增加省份,是什么原因?