code: public GroupHierarchyConfig subitems(InfrastructureItem... subitems) {
          checkNotNull(subitems, "List of server configs must be not a null");
          this.subitems.addAll(asList(subitems));
          return this;
      }
docs: Set sub items
  @param subitems items, that specified for group
  @return current {@link GroupHierarchyConfig} instance