code: protected Content getNavLinkTree() {
          Content linkContent = utils.isEnclosingPackageIncluded(typeElement)
                  ? getHyperLink(DocPath.parent.resolve(DocPaths.PACKAGE_TREE), contents.treeLabel)
                  : getHyperLink(pathToRoot.resolve(DocPaths.OVERVIEW_TREE), contents.treeLabel);
          Content li = HtmlTree.LI(linkContent);
          return li;
      }
docs: Get the tree link.
  
  @return a content tree for the tree link