主题：目录树问题

Dim ccb1 As WinForm.CheckedComboBox = e.Form.Controls("checkedcombobox1")

Dim dr As DataRow = DataTables("学校信息").find("单位全称='" & _usergroup &"'")

sszxx=dr("所属中心校")

Dim xxlist As String = DataTables("学校信息").sqlGetComboListString("单位全称","所属中心校='" & sszxx & "' and 学段='小学'")

Dim dt As DataTable

Dim cmd As New SQLCommand

cmd.cSEL   ECT DISTINCT 考试名称,单位名称,年级,班级  From {成绩} where 学段 ='小学' and 单位名称 in ('" & xxlist.replace("|",",") & "') order by 考试名称 desc"

dt = cmd.ExecuteReader()

Dim trv As WinForm.TreeView = e.Form.Controls("TreeView1")

trv.BuildTree(dt,"考试名称|单位名称|年级|班级","","考试名称 desc")

请问老师，上面这段没有产生目录树列表，该怎么改