Menu multinível com PHP/MySQL

function echo_menu($menu_array) {
    //go through each top level menu item
    foreach($menu_array as $menu) {
        echo "<li><a href='{$menu['link']}'>{$menu['titulo']}</a>";
        //see if this menu has children
        if(array_key_exists('children', $menu)) {
            echo '<ul>';
            //echo the child menu
            echo_menu($menu['children']);
            echo '</ul>';
        }
        echo '</li>';
    }
}

echo '<ul>';
echo_menu($menu_array);
echo '</ul>';