Leaves combine into one root
Transaction hashes form the leaves. Adjacent hashes are combined and hashed into parents until one Merkle root remains. Changing one byte changes the leaf, its ancestors and the root, binding the root to an ordered set of data.
A hash is not encryption: the transactions cannot be recovered from the root. Verification needs the original transaction and the neighbouring hashes for its branch.
A branch stays short
An inclusion proof needs one sibling hash from each level rather than the complete tree. The verifier combines them in the correct left-right order and compares the result with the root in the block header.
Proof length grows roughly with the logarithm of the number of leaves, so thousands of transactions need only a small number of hashes. Swapping left and right changes the result.
Inclusion is not full validation
A valid branch proves that a transaction belongs to the tree committed by a particular header. A client that also checks header linkage and proof of work can associate that commitment with a chain.
It does not check whether other transactions forged value, violated scripts or exceeded consensus limits. A full node validates the complete block, and an inclusion proof cannot prove that a peer did not omit some other fact.
Different trees commit to different things
The block header commits to the txid tree. SegWit adds a coinbase commitment to a wtxid tree, while Taproot commits optional script leaves through a tree that tweaks an output key.
These structures share a hashing idea but are not interchangeable. They bind different objects and use different serialization and domain rules, which implementations must follow exactly.