Function build 

pub fn build<F, H, R>(
    elements: &[F],
    batch_size: usize,
    salt_len: usize,
    rng: R,
) -> Result<BinaryMerkleTree<Output<H::LeafHash>, F>, Error>
where
    F: Field,
    H: HashSuite,
    R: Rng + CryptoRng,