Merkle tree is a fundamental part of blockchain technology. It is a mathematical data structure composed of hashes of different blocks of data, and which serves as a summary of all the transactions in a block. It also allows for efficient and secure verification of content in a large body of data. It also helps to verify the consistency and content of the data. Both Bitcoin and Ethereum use Merkle Trees structure. Merkle Tree is also known as Hash Tree.
The Merkle tree plays a vital role in blockchain technology. If someone needs to verify the existence of a specific transaction in a block, then there is no need to download the entire block to verify the transaction in a block. He can only download the chain of block headers. It allows downloading a collection of a branch of the tree which contains this transaction is enough. We check the hashes which are relevant to your transactions. If these hashes check out is correct, then we know that this particular transaction exists in this block.

Merkle trees, named after Ralph Merkle who patented the concept in 1979, are a fundamental component in blockchain technology. They play a crucial role in ensuring data integrity and efficient verification within a decentralized and distributed system like a blockchain.

A Merkle tree is a tree structure composed of hash values, where each leaf node represents a data block, and each non-leaf node is a hash of its child nodes. The tree is constructed by recursively hashing pairs of nodes until a single root hash, known as the Merkle root, is obtained. This Merkle root is then included in the block header of a blockchain.

The importance of Merkle trees in blockchain lies in several key aspects:

Efficient Verification: Merkle trees allow for efficient and quick verification of the integrity of a particular piece of data in a large dataset. Instead of comparing the entire dataset, users can verify the authenticity of a specific data block by checking only a small subset of hashes in the Merkle tree, leading to significant computational savings.
Consensus Mechanism: In a blockchain, the Merkle root is often included in the block header. This Merkle root is a summary or fingerprint of all the transactions within that block. By including this hash in the block header, participants in the network can agree on the content of the block without having to transmit all the individual transactions. This is particularly important for achieving consensus in a decentralized network.
Security: The cryptographic hash functions used in Merkle trees provide security against data tampering. Any change in the data of a single transaction would result in a change in the hash of the corresponding leaf node, affecting the hashes up the tree and ultimately altering the Merkle root. This makes it computationally infeasible to tamper with data without detection.
Lightweight Proofs: Merkle proofs, which involve providing a path of hashes from the target data block to the Merkle root, can be easily and efficiently shared. These proofs enable participants to verify the inclusion or absence of a specific transaction in a block without needing to possess the entire block or blockchain.

In summary, Merkle trees are a foundational concept in blockchain technology, providing a secure and efficient way to represent and verify the integrity of data within a decentralized and distributed ledger.