Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
   System.EventArgs) Handles MyBase.Load
        On Error Resume Next
        Dim TN As TreeNode
        For Each D As String In IO.Directory.GetDirectories("C:\")
            D = D.Substring(InStrRev(D, "\"))
            TN = New TreeNode(D)
            TN.Tag = "C:\" & D
 
            If IO.Directory.GetDirectories(TN.Tag).Length <> 0 Then
                TN.Nodes.Add("")
            End If
 
            TreeView1.Nodes.Add(TN)
        Next
    End Sub
 
    Private Sub TreeView1_MouseDown(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.MouseEventArgs) Handles TreeView1.MouseDown
        Dim TN As TreeNode = TreeView1.GetNodeAt(e.X, e.Y)
        If Not TN Is Nothing Then
            If TN.IsExpanded = False Then
                Fuellen(TN)
            End If
        End If
    End Sub
 
    Private Sub Fuellen(ByVal vTN As TreeNode)
        Dim TN As TreeNode
        With vTN
            .Nodes.Clear()
            For Each D As String In IO.Directory.GetDirectories(.Tag)
                D = D.Substring(InStrRev(D, "\"))
                TN = New TreeNode(D)
                TN.Tag = .Tag & "\" & D
 
                If IO.Directory.GetDirectories(TN.Tag).Length <> 0 Then
                    TN.Nodes.Add("")
                End If
 
                .Nodes.Add(TN)
            Next
        End With
    End Sub