vb使用目录树

    '******************************************************递归生成 treeview
    Private Sub LoadSubNodes(ByVal node_id As String, ByVal pNode As TreeNode)
        Dim Node As New TreeNode
        Dim tmpsql As String = "select * from wpfl where upid=" & node_id & ""
        Dim mycon = New OleDb.OleDbConnection(constr)
        Dim da = New OleDb.OleDbDataAdapter(tmpsql, mycon)
        Dim ds = New DataSet
        da.Fill(ds, "wpfl")
        For i As Integer = 0 To ds.Tables(0).Rows.Count - 1
            If pNode Is Nothing Then
                Node = Me.mytree.Nodes.Add(ds.Tables(0).Rows(i)("sx").ToString.Trim)
                Node.Tag = ds.Tables(0).Rows(i)("id").ToString.Trim
                LoadSubNodes(ds.Tables(0).Rows(i)("id"), Node)
            Else
                Node = pNode.Nodes.Add(ds.Tables(0).Rows(i)("sx").ToString.Trim)
                Node.Tag = ds.Tables(0).Rows(i)("id").ToString.Trim
                LoadSubNodes(ds.Tables(0).Rows(i)("id"), Node)
            End If
            Node.EnsureVisible()
        Next
    End Sub
    '******************************************************窗体载入
    Private Sub frmwpfl_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Call LoadSubNodes("0", Nothing)
        mytree.CollapseAll()
    End Sub
    '******************************************************树点击
    Private Sub mytree_AfterSelect(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewEventArgs) Handles mytree.AfterSelect
        bool_node = True
        If mytree.SelectedNode.Text <> "物品分类" Then