set current parent menui item

parent-menu-item.php

<?php
add_filter( 'wp_nav_menu_objects', 'add_menu_ancestor_parent_class' );
function add_menu_ancestor_parent_class( $items ) {

    // ancestor classes to find
    $ancestor = array('current-page-ancestor', 'current-post-ancestor');

    $parents = array();
    foreach ( $items as $item ) {
        if ( array_intersect( $ancestor , $item->classes)  ) {
            $parents[] = $item->menu_item_parent;
        }
    }
    // add class to ancestor parent menu item
    foreach ( $items as $item ) {
        if ( in_array( $item->ID, $parents ) ) {
            $item->classes[] = 'current-menu-ancestor'; 
        }
    }

    return $items;    
}