Eric Lippert's challenge - cleanerer

sealed class Dumper
{
    static public string Dump(Node root)
    {
        return Dump( root, "" );
    }
    static private string Dump(Node node, string indent)
    {
        return node.Text + "\n" +
            ( node.Children.Count == 0
                ? "" : node.Children.Take(node.Children.Count - 1).
                            Aggregate(string.Empty, (results, child) =>
                                results + indent + "├─" + Dump(child, indent + "│ ") )
              + indent + "└─" + Dump(node.Children.Last(), indent + "  " ) );
    }
}