if (parentIndex != 0) {
        /*
         * This is a guard for the case of the childless aunt node. Since the end of the array is
         * actually the middle of the heap, a smaller childless aunt node can become a child of x
         * when we bubble up alternate levels, violating the invariant.
         */
        int grandparentIndex = getParentIndex(parentIndex);
        int auntIndex = getRightChildIndex(grandparentIndex);