function createJsonTree($array, $currentParent, $currLevel = 0, $prevLevel = -1) {
 foreach ($array as $categoryId => $category) {
  if ($currentParent == $category['parent']) {      
   if ($currLevel > $prevLevel) $output .= ' , "children":[ '; 
   if ($currLevel == $prevLevel) $output .= " }, ";
    $output .= '{ "data" :'.'"'.$category['menu_title'].'"';
   if ($currLevel > $prevLevel) { $prevLevel = $currLevel; }
   $currLevel++; 
    $output .= self::createJsonTree($array, $category['id'], $currLevel, $prevLevel);
    $currLevel--;      
  } 
 }
 if ($currLevel == $prevLevel) $output .= " }] ";
 return $output;
}