Add hierarchy option to posts

If you need to have a parent option for any post custom post to organize inside the admin menu or to loop all child post for some post id just add this code snippet to functions.php

<?php
add_filter( 'register_post_type_args', 'add_hierarchy_support', 10, 2 );
function add_hierarchy_support( $args, $post_type ){
    if ($post_type === 'post' || $post_type === 'docs') { // <-- enter desired post type here
        $args['hierarchical'] = true;
        $args['supports'] = array_merge($args['supports'], array ('page-attributes') );
    }
    return $args;
}