Private Sub Trv_NodeMouseClick(sender As Object,
            e As TreeNodeMouseClickEventArgs) Handles Trv.NodeMouseClick
        dtx.Clear()
        'Level = 1: zweite Knotenebene
        If e.Node.Level = 1 Then
            Dim rows As DataRow() = DirectCast(e.Node.Tag, DataRow())
            For i As Integer = 0 To rows.Length - 1   "rows.Lenggth ist 6
                dtx.Rows.Add(rows(i).ItemArray)       "ItemArray Length ist 14 
            Next i
        End If
    End Sub