Anybody can help me add the tabs for panel of reports?

In "cms\code\Report.php" for function getCMSFields I tried add this code:

      $fields = new FieldSet(
         new TabSet("Root",
            new Tab("Report", _t('Report.REPORT', "Report"),
                  new LiteralField('ReportTitle1', "<h3>{$this->title()}</h3>"),
            )
         )
      );

, but result is empty. Many thanks!

Silverstripe v2.4