Eric Lippert's challenge

sealed class Dumper
{
    static public string Dump(Node root)
    {
        return root.Text + "\n" + DumpChildren( root, "" );
    }
    static private string DumpChildren(Node node, string indent)
    {
        return node.Children.Count > 0
            ?   string.Join( "",  node.Children.Take(node.Children.Count - 1).ToList()
                    .ConvertAll( new Converter<Node, String>( child => string.Format("{0}├─{1}\n{2}", indent, child.Text, DumpChildren(child, indent + "│ ") ) ) ).ToArray() )
                + string.Format("{0}└─{1}\n{2}", indent, node.Children.Last().Text, DumpChildren(node.Children.Last(), indent + "  ") )
            : "";
    }
}