How to use a start_el variable in start_lvl

On top of the sub-menu list items i would like to insert a <h2>parent-description</h2> line which i expect to show the description (or the title if wanted) of the parent item. Such as;

<ul>
   <li>
      <a href="">German Cars</a>
      <ul>
         <li><a href="">BMW</a></li>
         <li><a href="">Mercedes</a></li>
         <li><a href="">Volkswagen</a></li>
      </ul>
   </li>
   <li>
      <a href="">American Cars</a>
      <ul>
         <li><a href="">Chrysler</a></li>
         <li><a href="">Ford</a></li>
         <li><a href="">General Motors</a></li>
      </ul>
   </li>
</ul>

should look like

<ul>
   <li> <!-- $item->description of this list item has to be passed to start_lvl -->
      <a href="">German Cars</a>
      <ul>
         <h2>Cars Made in Germany </h2> <!--parent list item's description shows here-->
         <li><a href="">BMW</a></li>
         <li><a href="">Mercedes</a></li>
         <li><a href="">Volkswagen</a></li>
      </ul>
   </li>
   <li>
      <a href="">American Cars</a>
      <ul>
         <h2>Cars Made in the USA</h2> <!--parent list item's description shows here-->
         <li><a href="">Chrysler</a></li>
         <li><a href="">Ford</a></li>
         <li><a href="">General Motors</a></li>
      </ul>
   </li>
</ul>

What i know;

• I have basic knowledge on how to modify the walker by extending to walker_nav_menu.


• I know that to insert the <h2>parent-description</h2> after the <ul> and before the <li>s i have to concatenate the $output var of the start_lvl method.


• I know that the $item->description value is avalable within the start_el method.

What i don't know is, how to pass the $item->description value of start_el method (which is used one previously) to the start_lvl method at the time it produces the <ul> tag for list items to follow.

From some previous questions and answers here I implemented something like this but it didn't work.

class My_Nav_Walker extends Walker_Nav_Menu {
   private $curItem;

  function start_lvl(&$output, $depth = 0, $args = array()) {
     $indent = ( $depth > 0  ? str_repeat( "\t", $depth ) : '' );
     $output .= "\n" . $indent . '<ul>' . '<h2>' . $this->curItem->description . '</h2>"\n";
  }

  function start_el(&$output, $item, $depth = 0, $args = array(), $id = 0) {
    $this-> curItem = $item;
  }
}

Any helps highly appreciated.