public CacheNode getChild(String name) {
      if (name.startsWith("root.")) {
        name = name.substring("root.".length());
      }
      return children.get(name);
    }
@return key is path contains wildcard between each node
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/schema/ttl/TTLCache.java