void serializeChildren(final DataOutputStream outputStream) throws IOException {
    for (final PathPatternNode<V, S> childNode : children.values()) {
      childNode.serialize(outputStream);
    }
  }
Serialize PathPatternNode

<ul>
  <li>[required] 1 string: name. It specifies the name of node
  <li>[required] 1 int: nodeType or size of valueSet.
      <ul>
        <li>If this node is being used by PathPatternTree, it specifies the type of this node.
            -1 means from root to the current node is a registered path pattern. Otherwise -2.
        <li>If this node is being used by PatternTreeMap, it specifies the size of valueSet
            which will be serialized next.(>=0)
      </ul>
  <li>[optional] valueSet
  <li>[required] 1 int: children size.
  <li>[optional] children
</ul>
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/path/PathPatternNode.java