What Is the Function of the Merkle Tree in a Bitcoin Block?

The Merkle Tree, or hash tree, is a data structure used to efficiently summarize all transactions in a block. It works by repeatedly hashing pairs of transaction hashes until a single hash, the Merkle Root, remains.

The Merkle Root is included in the block header. Its primary function is to allow quick and secure verification that a specific transaction is included in a block without having to download all block data.