code: protected Integer getTotalNumberOfChildren() {
          Integer numChildrenNodes = 0;
          for (Level childLevel : levels) {
              numChildrenNodes += childLevel.getTotalNumberOfChildren();
          }
          return nodes.size() + numChildrenNodes;
      }
docs: Gets the total number of Children nodes for the level and its child levels.
  
  @return The total number of child nodes for the level and child levels.