code: protected void addLevelInfo(ClassDoc parent, List<ClassDoc> list,
              boolean isEnum, Content contentTree) {
          int size = list.size();
          if (size > 0) {
              Content ul = new HtmlTree(HtmlTag.UL);
              for (int i = 0; i < size; i++) {
                  ClassDoc local = list.get(i);
                  HtmlTree li = new HtmlTree(HtmlTag.LI);
                  li.addAttr(HtmlAttr.TYPE, LI_CIRCLE);
                  addPartialInfo(local, li);
                  addExtendsImplements(parent, local, li);
                  addLevelInfo(local, classtree.subs(local, isEnum),
                          isEnum, li);   // Recurse
                  ul.addContent(li);
              }
              contentTree.addContent(ul);
          }
      }
docs: Add each level of the class tree. For each sub-class or
  sub-interface indents the next level information.
  Recurses itself to add subclasses info.
  
  @param parent the superclass or superinterface of the list
  @param list list of the sub-classes at this level
  @param isEnum true if we are generating a tree for enums
  @param contentTree the content tree to which the level information will be added