主题：BuildTree功能自动过滤了空值问题

 你可以用sql语句，把空值替换成一个字符，如

select iif(第一列 is null, '空值', 第一列)

 然后再生成dt，再生成目录树。

非递归，代码

Dim tr As WinForm.TreeView = e.Form.Controls("TreeView1")
Dim Nd = tr.Nodes.Add("全部内容")

Dim dt As DataTable = DataTables("表a")
Dim cs As String = "第一列|第二列"
Dim nds As new List(Of WinForm.TreeNode)
For i As Integer = 0 To 3
    nds.Add(nd)
Next
For Each arys As String() In dt.GetValues(cs, "", cs.Replace("|", ","))
    Dim flag As Boolean = False
    For i As Integer = 0 To arys.Length - 1
        If nds(i+1).Name <> arys(i) OrElse flag Then
            flag = True
            nds(i+1) = nds(i).Nodes.Add(arys(i))
        End If
    Next
Next

 呃，你可以替换掉arys(i)的值，想怎么处理都行。

 关键代码 nds(i+1) = nds(i).Nodes.Add(arys(i))