addOverview.php

<?php
// Add overview link to navbar children
function main_menu_block_tree_alter(&$tree, &$config) {
  // Header Menu Block
  if($config['delta'] == 1) {

    foreach($tree as &$menu_item) {
      // Add overview link
      if(!empty($menu_item['below'])) {
        // Title of the new link
        $overview_title = $menu_item['link']['link_title'];

        // Link container
        $overview_link = array($overview_title => array("link" => array(), 'below' => array()));

        // Populate link data
        $overview_link[$overview_title]['link']['link_title']      = $overview_title;
        $overview_link[$overview_title]['link']['title']           = $overview_title;
        $overview_link[$overview_title]['link']['menu_name']       = $menu_item['link']['menu_name'];
        $overview_link[$overview_title]['link']['link_path']       = $menu_item['link']['link_path'];
        $overview_link[$overview_title]['link']['router_path']     = $menu_item['link']['router_path'];
        $overview_link[$overview_title]['link']['href']            = $menu_item['link']['href'];
        $overview_link[$overview_title]['link']['access']          = $menu_item['link']['access'];
        $overview_link[$overview_title]['link']['hidden']          = 0;
        $overview_link[$overview_title]['link']['has_children']    = 0;
        $overview_link[$overview_title]['link']['in_active_trail'] = 0;
        $overview_link[$overview_title]['link']['mlid']            = $menu_item['link']['mlid'];

        // Prepend link to menu
        $menu_item['below'] = $overview_link + $menu_item['below'];
      }
    }
  }
}
?>