!!! Overview[1]
[{$pagename}] is a tree in which every [non-leaf] node is labelled with the [hash] of the labels or values (in case of leaves) of its child nodes. 

[Hash] trees allow efficient and secure verification of the contents of large data structures. [Hash] trees are a generalization of hash lists and hash chains.

Demonstrating that a [leaf] node is a part of the given hash tree requires processing an amount of data proportional to the logarithm of the number of nodes of the tree;[1] this contrasts with hash lists, where the amount is proportional to the number of nodes.

The concept of hash trees is named after [Ralph Merkle] who patented it in [1979|Year 1979]

[{$pagename}] is a [Distributed Ledger Technology] ([DLT]) and the underpinnings of most [Blockchain] type implementations.

!! Common Uses
[Hash] trees can be used to verify any kind of data stored, handled and transferred in and between computers. 

Currently the main use of hash trees is to make sure that data blocks received from other peers in a peer-to-peer network are received undamaged and unaltered, and even to check that the other peers do not lie and send fake blocks. 

Suggestions have been made to use [hash] trees in trusted computing systems.[4] 

[Hash] trees are used in the 
* [IPFS] file system
* [Btrfs] file system
* [ZFS] file system  
* [BitTorrent] [protocol]
* [Apache Wave] [protocol]
* [Git] distributed revision control system
* [Tahoe-LAFS] backup system
* [Merkle Trees] including 
** [Blockchain]
** [Bitcoin] peer-to-peer network
** [Ethereum] peer-to-peer network
* [Certificate Transparency] framework
* a number of [NoSQL] systems like [Apache Cassandra], [Riak] and [DynamoDB].[9]

The original purpose of hash trees was to make it possible to efficiently handle many Lamport one-time signatures. Each Lamport key can only be used to sign a single message, but combined with hash trees they can be used for many messages, becoming a fairly efficient digital signature scheme known as a Merkle signature scheme.


!! More Information
There might be more information for this subject on one of the following:
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* [#1] - [Merkle_tree|Wikipedia:Merkle_tree|target='_blank'] - based on data observed:2015-05-18