*/
    @Nullable MoveDesc<E> tryCrossOverAndBubbleUp(int removeIndex, int vacated, E toTrickle) {
      int crossOver = crossOver(vacated, toTrickle);
      if (crossOver == vacated) {
        return null;
      }
      // Successfully crossed over from min to max.
      // Bubble up max levels.
      E parent;

     */
    @Nullable MoveDesc<E> tryCrossOverAndBubbleUp(int removeIndex, int vacated, E toTrickle) {
      int crossOver = crossOver(vacated, toTrickle);
      if (crossOver == vacated) {
        return null;
      }
      // Successfully crossed over from min to max.
      // Bubble up max levels.
      E parent;