Get information about a menu item
MenuTreeParameters::$expandedParents are a list of menu tree ids (a composite key of the menu bundle and the menu content UUID). You can see its data in the menu_tree, menu_link_content, menu_link_content_data, database tables. 

If you need to programmatically invoke the menu item for reference, you can load it via Drupal's entity manager:

// Load each menu content item per UUID
foreach ($parents as $menu_uuid) {
  $menu_content = current(\Drupal::entityManager()-&gt;getStorage('menu_link_content')-&gt;loadByProperties(array('uuid' =&gt; $menu_uuid)));
  // @TODO: Reference menu content properties for data
  // (e.g. $menu_content-&gt;get('title')-&gt;value / $menu_content-&gt;get('link')
}