The UTXO model consists of a forest structure that tracks the history of a unit. Roots are coin-creation events, such as rewards obtained from PoW or PoS, and have no input transactions. By definition, all leaves are unspent transaction outputs. When a leaf branches or sprouts a new limb, the leaf becomes an inner node of the graph. During this process, the unspent transaction output is consumed and used as the input of a new unspent transaction output. Using this model, one can transparently trace back the history of each transaction through the public ledger. The UTXO model inherently allows for parallel processing capabilities to initialize transactions among multiple addresses, indicating its scalability.