code: protected void generatePackageTreeFile() throws IOException {
          Content body = getPackageTreeHeader();
          Content headContent = getResource("doclet.Hierarchy_For_Package",
                  Util.getPackageName(packagedoc));
          Content heading = HtmlTree.HEADING(HtmlConstants.TITLE_HEADING, false,
                  HtmlStyle.title, headContent);
          Content div = HtmlTree.DIV(HtmlStyle.header, heading);
          if (configuration.packages.length > 1) {
              addLinkToMainTree(div);
          }
          body.addContent(div);
          HtmlTree divTree = new HtmlTree(HtmlTag.DIV);
          divTree.addStyle(HtmlStyle.contentContainer);
          addTree(classtree.baseclasses(), "doclet.Class_Hierarchy", divTree);
          addTree(classtree.baseinterfaces(), "doclet.Interface_Hierarchy", divTree);
          addTree(classtree.baseAnnotationTypes(), "doclet.Annotation_Type_Hierarchy", divTree);
          addTree(classtree.baseEnums(), "doclet.Enum_Hierarchy", divTree);
          body.addContent(divTree);
          addNavLinks(false, body);
          addBottom(body);
          printHtmlDocument(null, true, body);
      }
docs: Generate a separate tree file for each package.