// Bubble up max levels.
      E parent;
      // If toTrickle is moved up to a parent of removeIndex, the parent is
      // placed in removeIndex position. We must return that to the iterator so
      // that it knows to skip it.
      if (crossOver < removeIndex) {
        // We crossed over to the parent level in crossOver, so the parent
        // has already been moved.
        parent = elementData(removeIndex);
      } else {