ORAM stands for Oblivious RAM is a cryptographic primitive allowing updates to data (stored in a tree) in a manner that does not allow for access patteren leakage
If we had a normal tree much like most of the implementations a user might observe update history of it's sibling (included in the merkle proof) and link the transactions to onchain data for same amount.
This is a access pattern leakage attach. This implemenation is based on ORAM-based SMT introduced in the DAPOL + the implementation is adapted to our usecase of Proof of Solvency in case of a blockchain custodian