private void PrintRecursive(TreeNode treeNode)
{
   // Print the node.
   System.Diagnostics.Debug.WriteLine(treeNode.Text);
   MessageBox.Show(treeNode.Text);
   // Print each node recursively.
   foreach (TreeNode tn in treeNode.Nodes)
   {
      PrintRecursive(tn);
   }
}

// Call the procedure using the TreeView.
private void CallRecursive(TreeView treeView)
{
   // Print each node recursively.
   TreeNodeCollection nodes = treeView.Nodes;
   foreach (TreeNode n in nodes)
   {
      PrintRecursive(n);
   }
}