/**
    * Return the entire site tree as a nested UL.
    * @return string HTML for site tree
    */
   public function SiteTreeAsUL() {

      $obj = singleton('Folder');
      $obj->setMarkingFilter('ClassName', ClassInfo::subclassesFor('Folder'));
      $obj->markPartialTree(30, null, "ChildFolders");

      if($p = $this->currentPage()) $obj->markToExpose($p);

      // getChildrenAsUL is a flexible and complex way of traversing the tree
      $siteTreeList = $obj->getChildrenAsUL(
         '',
         '"<li id=\"record-$child->ID\" class=\"$child->class" . $child->markingClasses() . ($extraArg->isCurrentPage($child) ? " current" : "") . "\">" . ' .
         '"<a href=\"" . Controller::join_links(substr($extraArg->Link(),0,-1), "show", $child->ID) . "\" class=\"" . ($child->hasChildFolders() ? " contents" : "") . "\" >" . $child->TreeTitle() . "</a>" ',
         $this,
         true,
         "ChildFolders"
      );   

      // Wrap the root if needs be
      $rootLink = $this->Link() . 'show/root';
      $baseUrl = Director::absoluteBaseURL() . "assets";
      if(!isset($rootID)) {
         $siteTree = "<ul id=\"sitetree\" class=\"tree unformatted\"><li id=\"record-root\" class=\"Root\"><a href=\"$rootLink\"><strong>{$baseUrl}</strong></a>"
         . $siteTreeList . "</li></ul>";
      }

      return $siteTree;
   }