Adding search to navigation bar

I am trying to add a search box to my navigation bar. It works but I have a mega menu. So anything below it will have search boxes also. Is there a way to only display it in the main nav bar?

add_filter('wp_nav_menu_items','add_search_box', 10, 2);
function add_search_box($items, $args) {
if ($args->theme_location == 'First Menu' || 'Second Menu') {
ob_start();
get_search_form();
$searchform = ob_get_contents();
ob_end_clean();

$items .= '<li class="mega-menu-item mega-menu-item-type-custom mega-menu-item-object-custom mega-menu-item-1173">' . $searchform . '</li>';

}
return $items;
}