public function render(array $tree, $level = 0)
    {
        $output = '';

        foreach ($tree as $label => $next)
        {

            if (is_string($next))
            {
                $label = $next;
            }

            // Output the label
            $output .= sprintf("%s- %s\n", str_repeat(' ', $level * $this->_padding), $label);

            // Next level
            if (is_array($next))
            {
                $output .= $this->render($next, $level + 1);
            }

        }

        return $output;
    }