An example Bitcoin private key
L1VmqTKdwzM361jkFVAT5Dd2b3APSQEW6bHs8TG2XCrGj2qVRSBb
That's in compressed Wallet Import Format, but that particular private key is invalid.
Merkle Trees - Once hashed it will look like this:
2d94683fa2f8aaae4a6f377d93b875f680adf96b9c3e9577554b742f412fa9ad
I think you are confused here. Private keys undergo ECDSA to give a public key, but they aren't hashed, and they certainly aren't hashed to Merkle Trees.
and decryption of a hash is much harder work, numerous times harder, 1,000,000 and more.
It's not "numerous times harder", it's impossible. Hashing is not the same as encryption. You can't "decrypt" a hash. Nor can you reverse it. It is a one way process.
Yes, first I was confused, but I realized, that hashed input on merkle tree is based on transaction data which is encrypted.
And yes, there is no data to decrypt the private key, miners don't have any input information to decrypt private keys, so there is no way to make some computations to find out the private key, it will be just a random guess, which is nearly to impossible to find a correct key.
I was confused, because miners do some computations or a lot of guesses per second to find a hash. Since miners try to find a random hash for pow, it will be much harder to find a specific one in case with private keys.