How to select all the visible nodes in WinForms TreeViewAdv?

private void button1_Click(object sender, System.EventArgs e)
{
   foreach (TreeNodeAdv node in this.treeViewAdv1.Root.Nodes)
   {
      this.treeViewAdv1.SelectedNodes.Add(node);
      TreeNodeAdv lastNode = node.LastNode;
      while (lastNode != null)
      {
          this.treeViewAdv1.ExtendSelectionTo(lastNode);
          lastNode = lastNode.LastNode;
      }
   }
   this.treeViewAdv1.Focus();
}

Private Sub button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
For Each node As TreeNodeAdv In Me.treeViewAdv1.Root.NodesMe.treeViewAdv1.SelectedNodes.Add(node)
    Dim lastNode As TreeNodeAdv = node.LastNode
    Do While Not lastNode Is Nothing 
        Me.treeViewAdv1.ExtendSelectionTo(lastNode)
        lastNode = lastNode.LastNode
        Loop
    Next node
    Me.treeViewAdv1.Focus()
End Sub