主题：请看一下公式那里有错

Dim tr As winform.treeview
Dim nd1 As winform.treenode
Dim nd2 As winform.treenode
tr = e.Form.controls("treeview1")
Dim cmd As new sqlcommand
Dim dt,dt2 As DataTable
cmd.CommandText = "SELECT DISTINCT 产品,客户 From {订单}"
dt = cmd.ExecuteReader()
dt2 = dt
nd1 = tr.nodes.add("a1","按产品")
For Each dr As DataRow In dt.DataRows
nd1 = tr.nodes.add("0101",dr("产品"))
Next
nd1 = tr.nodes.add("a2","按客户")
For Each dr As DataRow In dt.DataRows
nd1 = tr.nodes.add("0101",dr("客户"))
Next
tr.expandall()

根据以上公式在订单表中可以生成目录树，但没有卷展，应该怎么改