Merkle tree also known as hash tree, is a hashes of hashes structured in hierarchical order. Merkle tree contains hashes of blocks of transactions. Hash is a function that turns any length of data into a fixed length output. A Bitcoin block hash looks like this: “0000000000000000002246fbbc26c31f4fef2b2c05a39a81f237605741988aec”.
Each bitcoin transactions has its own hash. Then each of those transaction hashes are hashed together, which eventually creates one single hash for an entire block. Merkle Tree was invented by Ralph Merkle in 1979. Merkle trees are used in blockchains because they allow anyone to confirm the validity of a transaction without downloading the whole blockchain.