主题：目录树与数据表的问题求助

Dim tr As WinForm.TreeView
Dim nd As WinForm.TreeNode
tr = e.Form.Controls("TreeView1")
nd = tr.SelectedNode
If nd IsNot Nothing Then
    If nd.Level = 2 Then
        MessageBox.Show("最多允许三层节点!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)
    Else
        Dim dr As DataRow = DataTables("表A").AddNew
        If nd.Level = 0 Then
            dr("大类") = nd.Text
            dr("二类") = "二类"

            nd = nd.Nodes.Add("二类")
        ElseIf nd.Level = 1
            dr("大类") = nd.ParentNode.Text
            dr("二类") = nd.text
            dr("三类") = "三类"

            nd = nd.Nodes.Add("三类")
        End If
        tr.SelectedNode = nd
        tr.Select()
        tr.BeginEdit()
    End If
End If