Function merkle_add_internal 

pub fn merkle_add_internal(
    db_info: DbHandle,
    db_roots: DbHandle,
    root_key: &[u8],
    tree_key: &[u8],
    elements: &[MerkleNode],
    local: bool,
) -> GenericResult<()>

Internal function for merkle_add which branches to either on-chain or transaction-local.