参考这种:
http://www.foxtable.com/webhelp/topics/0917.htm
Dim cmd As New SQLCommand
Dim dt As DataTable
cmd.CommandText = "Select Distinct Year(合同起始日) As 年 From {合同主表}"
dt = cmd.ExecuteReader()
Dim trv As WinForm.TreeView = e.Form.Controls("TreeView1")
trv.BuildTree(dt, "年")
trv.Nodes.Insert("显示所有行",0)