Function merkle_add 

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

Add given elements into a Merkle tree. Used for inclusion proofs.

• db_info is a handle for a database where the Merkle tree is stored.
• db_roots is a handle for a database where all the new Merkle roots are stored.
• root_key is the serialized key pointing to the latest Merkle root in db_info
• tree_key is the serialized key pointing to the Merkle tree in db_info.
• elements are the items we want to add to the Merkle tree.

There are 2 databases:

• db_info stores general metadata or info.
• db_roots stores a log of all the merkle roots.

Inside db_info we store:

• The [latest root hash:32] under root_key.
• The incremental merkle tree under tree_key.

Inside db_roots we store:

• All [merkle root:32]s as keys. The value is the current [tx_hash:32][call_idx:1]. If no new values are added, then the root key is updated to the current (tx_hash, call_idx).