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