code: protected Content getNavLinkMainTree(String label) {
          Content mainTreeContent = getHyperLink(pathToRoot.resolve(DocPaths.OVERVIEW_TREE),
                  new StringContent(label));
          Content li = HtmlTree.LI(mainTreeContent);
          return li;
      }
docs: Get the overview tree link for the main tree.
  
  @param label the label for the link
  @return a content tree for the link