code: protected void addLinkToMainTree(Content div) {
          Content span = HtmlTree.SPAN(HtmlStyle.packageHierarchyLabel,
                  getResource("doclet.Package_Hierarchies"));
          div.addContent(span);
          HtmlTree ul = new HtmlTree (HtmlTag.UL);
          ul.addStyle(HtmlStyle.horizontal);
          ul.addContent(getNavLinkMainTree(configuration.getText("doclet.All_Packages")));
          div.addContent(ul);
      }
docs: Add a link to the tree for all the packages.
  
  @param div the content tree to which the link will be added