Dumper.Dump

sealed class Dumper
{
    static public string Dump(Node root)
    {
        StringBuilder builder = new StringBuilder();
        builder.AppendLine(root.Text);
        DumpChildren(builder, "", root);
        return builder.ToString();
    }
    static private void DumpChildren(StringBuilder builder, string prefix, Node node)
    {
        for (int i=0; i != node.Children.Count; ++i)
        {
            Node child = node.Children[i];
            bool isLast = i == node.Children.Count - 1;
            string nodePrefix = prefix + (isLast ? "└─" : "├─");
            string childPrefix = prefix + (isLast ? "  " : "│ ");
            builder.AppendLine(nodePrefix + child.Text);
            DumpChildren(builder, childPrefix, child);
        }
    }
}