public CacheNode addChild(String name, long ttl) {
      CacheNode newNode = new CacheNode(name, ttl);
      children.put(name, newNode);
      return newNode;
    }
@return key is path contains wildcard between each node
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/schema/ttl/TTLCache.java