public long getMask() {
    return mask;
  }
Tree node which data shuffle into, consist of two parts.

<ul>
  <li>mask: mask code representing the height of tree, validate value:2^n-1(n representing the
      height of tree)
  <li>index: index of tree node(starting from 0)
</ul>

<p>index = hashCode(data) & mask;
amoro-format-iceberg/src/main/java/org/apache/amoro/data/DataTreeNode.java