code: public static <T extends HierarchyEntity<T, ?>> Map<T, String> sort(List<T> datas) {
      return sort(datas, null);
    }
docs: 按照上下关系排序
  
  @param datas a {@link java.util.List} object.
  @param <T> a T object.
  @return a {@link java.util.Map} object.