wordpress-nav-array.php

<?php
/**
* Modification of "Build a tree from a flat array in PHP"
*
* Authors: @DSkinner, @ImmortalFirefly and @SteveEdson
*
* @link http://stackoverflow.com/a/28429487/2078474
*/
function buildTree( array &$elements, $parentId = 0 )
{
   $branch = array();
   foreach ( $elements as &$element )
   {
       if ( $element->menu_item_parent == $parentId )
       {
           $children = buildTree( $elements, $element->ID );
           if ( $children ){
               $element->has_children = 1;
               $element->children = $children;
           } else {
               $element->has_children = 0;
           }

           $branch[$element->ID] = $element;
           unset( $element );
       }
   }
   return $branch;
}

/**
* Transform a navigational menu to it's tree structure
*
* @uses  buildTree()
* @uses  wp_get_nav_menu_items()
*
* @param  String     $menud_id
* @return Array|null $tree
*/
function wpse_nav_menu_2_tree( $menu_id )
{
   $items = wp_get_nav_menu_items( $menu_id );
   return  $items ? buildTree( $items, 0 ) : null;
}

/**
* Call to func
*/

$menu = wpse_nav_menu_2_tree( $menu_id );
print_r($menu);