Merkle Tree

A Merkle Tree connects the hashes for all of the transactions in a block with each other via branches. Once connected these hashes are condensed into a single hash known as a Merkle Root. The Merkle Root is then stored in the block instead of storing the transactions individually. 

This allows blockchains to efficiently process and store transactions. Instead of confirming transactions piecemeal as they occur. Blockchains employ Merkle Trees to group transactions together and confirm them via batch processing. 

Beyond the burden confirming transactions individually would impose on blockchains. Absent Merkle Trees it would be almost impossible to verify a blockchains history without extensive computing power well past the limits of most individuals. 

An additional benefit is grouping transactions together this way enhances network security. If any transaction in the Merkle Root hash is tampered with. The value for the entire Merkle Root will change not just the value of the individual transaction. Ensuring the blockchain will reject the malicious activity since its triggering a change to a previously verified Merkle Root.

Further Reading Merkle Trees

Merkle Tree in Blockchain: What is it and How does it work