Creating a navigation menu of all posts of a custom post type and their children posts?

Here is the general logic that can be used to fetch the child custom posts

What I’ve assumed here is, You create a county post, then you create a area post and from parent metabox you select the desired county post and save the post id in post_parent

function wpse_128630_cp( $post_type="county", $post_parent="", $posts_per_page = -1 ){
  $args = array(
    'post_type' => $post_type,
    'post_status' => 'publish',
    'posts_per_page' => $posts_per_page,
            'post_parent' => $post_parent ,
    'order' => 'desc'
 );
 $menu = new WP_Query( $args );
 if(!empty($menu)) { return $menu;}
 else{
    //To debug, uncomment below code
    //echo "<pre>";
    //print_r($menu);
    //echo "</pre>";
 }
}
<ul class="wpse-parent menu">
<?php $menu = wpse_128630_cp();
while ( $menu->have_posts() ) : $menu->the_post(); ?>
<li class="menu-item">
    <a href="https://wordpress.stackexchange.com/questions/128630/<?php the_permalink(); ?>"><?php the_title(); ?></a> <?php
        $submenu = wpse_128630_cp( 'area', get_the_ID() ); 
        if(!empty($submenu)){ ?>
            <ul class="wpse-sub-menu menu"> <?php
                while ( $submenu->have_posts() ) : $submenu->the_post(); ?>
                    <li class="menu-item">
                        <a href="<?php $submenu->the_permalink(); ?>"><?php $submenu->the_title(); ?></a>
                    </li>
                <?php endwhile; ?>
            </ul><?php
        }?>
  </li>
  <?php endwhile; ?>
  </ul>