protected final R transferToResult(final N node) {
    return collectMNode(node);
  }
This class defines any node in MTree as potential target node. On finding a path matching the
given pattern, if a level is specified and the path is longer than the specified level,
MNodeLevelCounter finds the node of the specified level on the path and process it. The same node
will not be processed more than once. If a level is not given, the current node is processed.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/schemaregion/mtree/traverser/collector/MNodeCollector.java