Organize all menus with their respectives submenus.

create_menu_with_submenu_wordpress.php

<?php
function generateMenu ()
{
  $array_menu = wp_get_nav_menu_items('main-menu');

  $menu    = [];
  $submenu = [];
  foreach ($array_menu as $item_menu) {
      if (empty($item_menu->menu_item_parent)) {
          $menu[$item_menu->ID] = [
            'ID'        => $item_menu->ID,
            'title'     => $item_menu->title,
            'url'       => $item_menu->url,
            'children'  => [],
          ];
      } else {
          $submenu[$item_menu->ID] = [
            'ID'    => $item_menu->ID,
            'title' => $item_menu->title,
            'url'   => $item_menu->url
          ];
          $menu[$item_menu->menu_item_parent]['children'][$item_menu->ID] = $submenu[$item_menu->ID];
      }
  }
  
  return $menu;
}
add_action('createMainMenu', 'generateMenu');


/*

Output example:

Array
(
    [80] => Array
        (
            [ID] => 80
            [title] => Quem somos
            [url] => http://wordpress.dev/quem-somos/
            [children] => Array
                (
                    [56] => Array
                        (
                            [ID] => 56
                            [title] => História
                            [url] => http://wordpress.dev/historia/
                        )

                    [97] => Array
                        (
                            [ID] => 97
                            [title] => Missão
                            [url] => http://wordpress.dev/missao/
                        )

                )

        )

    [79] => Array
        (
            [ID] => 79
            [title] => Exames
            [url] => http://wordpress.dev/exames/
            [children] => Array
                (
                )

        )

    [78] => Array
        (
            [ID] => 78
            [title] => Cirurgias
            [url] => http://wordpress.dev/cirurgias/
            [children] => Array
                (
                )

        )

    [77] => Array
        (
            [ID] => 77
            [title] => Corpo clinico
            [url] => http://wordpress.dev/corpo-clinico/
            [children] => Array
                (
                )

        )

    [76] => Array
        (
            [ID] => 76
            [title] => Convênios
            [url] => http://wordpress.dev/convenios/
            [children] => Array
                (
                )

        )

    [75] => Array
        (
            [ID] => 75
            [title] => Área médica
            [url] => http://wordpress.dev/area-medica/
            [children] => Array
                (
                )

        )

    [74] => Array
        (
            [ID] => 74
            [title] => Pré-agendamento
            [url] => http://wordpress.dev/pre-agendamento/
            [children] => Array
                (
                )

        )

    [58] => Array
        (
            [ID] => 58
            [title] => Contato
            [url] => http://wordpress.dev/contato/
            [children]
            
*/