Return the root element of the merkle tree.

def merkleroot(merkletree: 'MerkleTreeState') -> Locksroot:
    """ Return the root element of the merkle tree. """
    assert merkletree.layers, 'the merkle tree layers are empty'
    assert merkletree.layers[MERKLEROOT], 'the root layer is empty'

    return Locksroot(merkletree.layers[MERKLEROOT][0])