当单击节点时，选定的节点展开，同层的其它节点关闭。。

Dim nd As WinForm.TreeNode = trv.SelectedNode
Dim id As Integer = nd.index
If e.Node.Level = 0 Then
    Dim cnt As Integer  = trv.Nodes.Count - 1
    For i As Integer = cnt To 0 Step -1
        If trv.Nodes.Count >= 0 Then
            If i=id
                trv.Nodes(i).Expand()
            Else
                trv.Nodes(i).Collapse()
            End If
        End If
    Next

ElseIf e.Node.Level = 1 Then
    Dim cnt As Integer  = trv.Nodes.Count - 1
    For i As Integer = cnt To 0 Step -1
        If trv.Nodes.Count >= 0 Then
            If i=id
                trv.Nodes(i).Nodes(i).Expand()
            Else
                trv.Nodes(i).Nodes(i).Collapse()
            End If
        End If
    Next

End If

这个只能做到根节点，往下的就出错了。。。

用这个比较好：
 
http://www.foxtable.com/help/topics/2302.htm

大概就是这样：
 
Dim trv As WinForm.TreeView = e.Form.Controls("TreeView1")
For Each nd As WinForm.TreeNode In trv.AllNodes
    If nd.Level = e.Node.Level AndAlso nd.FullPath <> e.Node.FullPath then
        trv.Nodes(i).Collapse()
    End If
Next
e.Node.Expand()

。。。谢狐爸

Dim trv As WinForm.TreeView = e.Form.Controls("TreeView1")
If e.Node.Level = 0 Then
    Dim cnt As Integer  = trv.Nodes.Count - 1
    For i As Integer = cnt To 0 Step -1
        For Each nd As WinForm.TreeNode In trv.AllNodes
            If nd.Level = e.Node.Level AndAlso nd.FullPath <> e.Node.FullPath Then
                trv.Nodes(i).CollapseAll()
            Else
                e.Node.Expand()
            End If
        Next
    Next
ElseIf e.Node.Level = 1 Then
    Dim cnt As Integer  = trv.SelectedNode.ParentNode.Nodes.Count - 1
    For i As Integer = cnt To 0 Step -1
        For Each nd As WinForm.TreeNode In trv.AllNodes
            If nd.Level = e.Node.Level AndAlso nd.FullPath <> e.Node.FullPath Then
                trv.Nodes(Value(0)).Nodes(i).CollapseAll()
            Else
                e.Node.Expand()
            End If
        Next
    Next
ElseIf e.Node.Level = 2 Then
    Dim cnt As Integer  = trv.SelectedNode.ParentNode.Nodes.Count - 1
    For i As Integer = cnt To 0 Step -1
        For Each nd As WinForm.TreeNode In trv.AllNodes
            If nd.Level = e.Node.Level AndAlso nd.FullPath <> e.Node.FullPath Then
                trv.Nodes(Value(0)).Nodes(Value(1)).Nodes(i).CollapseAll()
            Else
                e.Node.Expand()
            End If
        Next
    Next
ElseIf e.Node.Level = 3 Then
    Dim cnt As Integer  = trv.SelectedNode.ParentNode.Nodes.Count - 1
    For i As Integer = cnt To 0 Step -1
        For Each nd As WinForm.TreeNode In trv.AllNodes
            If nd.Level = e.Node.Level AndAlso nd.FullPath <> e.Node.FullPath Then
                trv.Nodes(Value(0)).Nodes(Value(1)).Nodes(Value(2)).Nodes(i).CollapseAll()
            Else
                e.Node.Expand()
            End If
        Next
    Next
End If

可不可以简化代码   不管目录树的层数。。。？

单击展开，这样不就行了吗：

e.Node.Expand()