代码运行错误，到第二段时老提示无法创建子列表

Public Function addtree(ByVal ds As DataSet, ByVal treename As TreeNodeCollection, ByVal x1 As Integer) As Boolean
        Dim dt As DataTable = ds.Tables("Me.XMTN.客户分类")
        Dim dm As BindingManagerBase = Me.BindingContext(ds, "Me.XMTN.客户分类")
        Dim dr As DataRow() = dt.Select("Me.XMTN.客户分类.本级编号=" & x1.ToString)
        Dim dr1 As DataRow
        Dim nd As TreeNode

        Dim x2 As Integer
        If dr.GetLength(0) <> 0 Then
            For Each dr1 In dr
                nd = treename.Add(dr1("Me.XMTN.客户分类.类别名称"))
                nd.Tag = (dr1("Me.XMTN.客户分类.类别编号"))
                x2 = treename.IndexOf(nd)
                addtree(ds, treename.Item(x2).Nodes, dr1("Me.XMTN.客户分类.类别编号"))
            Next
        End If
        Return True
    End Function