code: public function getTemplate($page)
      {
          // determine page bundle name.
          $bundle = $this->getBundleName(ClassUtils::getRealClass(get_class($page)));
          return sprintf('%s:Page:%s.html.twig', $bundle, $page->getTemplateName());
      }
docs: Returns the template of the page from the bundle the entity is part of.
  
  @param PageInterface $page
  @return string
  
  @throws \RuntimeException