code: public Set<Map.Entry<String, V>> entrySet()
      {
          Set<Map.Entry<String, V>> entrySet = new TreeSet<Map.Entry<String, V>>();
          StringBuilder sb = new StringBuilder();
          for (BaseNode node : child)
          {
              if (node == null) continue;
              node.walk(new StringBuilder(sb.toString()), entrySet);
          }
          return entrySet;
      }
docs: 获取键值对集合
  
  @return