Example of data that is hashed in the merkle tree for a transaction
1) Transactions don't contain merkle hashes. Pre-SegWit transactions' hashes are calculated by serializing the transaction (you can search for "the hex format"), and then hashing the byte array. After SegWit, signatures are excluded from transaction hashes.

2) (I can't understand what you're asking for)

3) 1900 transactions is not so deep. The height can be calculated by ceil(log_2(number_of_tx))+1. Plug in 1900, and the height is 12. If you want to learn how merkle trees could be used for ISA, I'd suggest searching for MAST. It allows hiding the unexecuted parts of Script.