tree menu & sub-menu using codeigniter

Could you please explain this code

Code:

function ordered_menu($array,$parent_id = 0)
{
  $temp_array = array();
  foreach($array as $element)
  {
    if($element['parent_id']==$parent_id)
    {
      $element['subs'] = ordered_menu($array,$element['id']);
      $temp_array[] = $element;
    }
  }
  return $temp_array;
}