Add bookmark links to the wp_nav_menu

Add bookmark links to the wp_nav_menu.php

add_filter('wp_nav_menu_items', 'wps_add_bookmarks', 10, 2);
function wps_add_bookmarks($items, $args) {
        $cat = '2'; // define category
        $name = 'Bookmarks';
        $bookmarks = array();
        $bookmarks = get_bookmarks("category=$cat");
        if ($bookmarks[0] != '') {
            $items .= '<li><a href="#">'.$name.'</a><ul class="sub-menu">';
            foreach ( $bookmarks as $bookmark ) {
                $items .= '<li><a href="'.clean_url($bookmark->link_url).'"';
                if($bookmark->link_target){
                        $items .='target="'.$bookmark->link_target.'" ';}
                if($bookmark->link_rel){
                        $items .='rel="'.$bookmark->link_rel.'" ';}
                $items .= '>'.$bookmark->link_name.'</a></li>';
            }
            $items .= '</ul>';
          }
        return $items;
}