@Override
      Optional<BinaryNode> createTree(int size, Random rng) {
        if (size == 0) {
          return Optional.absent();
        } else {
          int leftChildSize = (size - 1) / 2;
          int rightChildSize = size - 1 - leftChildSize;
          return Optional.of(
              new BinaryNode(
                  rng.nextInt(), createTree(leftChildSize, rng), createTree(rightChildSize, rng)));
        }
      }

      @Override
      Optional<BinaryNode> createTree(int size, Random rng) {
        if (size == 0) {
          return Optional.absent();
        } else {
          int leftChildSize = (size - 1) / 2;
          int rightChildSize = size - 1 - leftChildSize;
          return Optional.of(
              new BinaryNode(
                  rng.nextInt(), createTree(leftChildSize, rng), createTree(rightChildSize, rng)));
        }
      }