Why org.hibernate.transaction.JDBCTransaction was removed from latest hibernate version?

Hello Team,

Why org.hibernate.transaction.JDBCTransaction was removed from latest hibernate versions ?
What is the alternative for the same in latest version of hibernate ?

In our application we are using hibernate 3.5 and JDBCTransaction class is extended with the below purpose mentioned :
Nested transaction used for all hibernate sessions
As per my understanding this class maintains the transactions count for the current session.
Please let me know if you wanted to see the code.

We are migrating hibernate from 3.5 to 5.1 and we do not found any alternative for this class.

Can anyone please reply on the above questions please ?