if ($mode == 'S' && is_object($tree)):
        $node = $tree->getRootTreeNodeObject();
        $node->populateChildren();
        if (is_object($node)) {
            $walk = function($node) use (&$walk, &$view, $selectedTopicID) {
                $i = 1;
             $a = 1;
                foreach($node->getChildNodes() as $topic) {
                    if ($topic instanceof \Concrete\Core\Tree\Node\Type\TopicCategory) { ?>
                  <?php if ($a > 1) { ?>
                     </ul></li></ul>
                  <?php }; ?>
                        <ul class="nav nav-stacked" id="accordion<?php echo $a; ?>"><li class="panel"><a data-toggle="collapse" data-parent="#accordion<?php echo $a; ?>" href="#Link<?php echo $a; ?>"><?php echo $topic->getTreeNodeDisplayName()?></a>
                    <?php } else { 
                  if ($i == 1) {?> 
                     <ul class="collapse" id="Link<?php echo $a;?>">
                  <?php }; ?>
                        <li class="list-unstyled"><a href="<?php echo $view->controller->getTopicLink($topic)?>"
                                <?php if (isset($selectedTopicID) && $selectedTopicID == $topic->getTreeNodeID()) { ?>
                                    class="ccm-block-topic-list-topic-selected"
                                <?php } ?> ><?php echo $topic->getTreeNodeDisplayName()?></a></li>
                        <?php $i++; ?>
                    <?php } ?>
               <?php $a++;?>
                    <?php $walk($topic); ?>
                <?php } 
            };
            $walk($node);
        }
 
    endif;