docs: public void appendSpecTopic(final SpecTopic specTopic) {
          topics.add(specTopic);
          nodes.add(specTopic);
          if (specTopic.getParent() != null && specTopic.getParent() instanceof Level) {
              ((Level) specTopic.getParent()).removeSpecTopic(specTopic);
          }
          specTopic.setParent(this);
      }