code: public void openFirstLevel() {
  
          if (!m_categories.isEmpty()) {
              for (int i = 0; i < m_scrollList.getWidgetCount(); i++) {
                  CmsTreeItem item = (CmsTreeItem)m_scrollList.getItem(i);
                  item.setOpen(true);
              }
          }
      }
docs: Opens the first level in the categories tree.<p>