Basically my main task has several sub tasks of Level 1. One of those sub tasks need to have several more sub tasks of Level 2
In other words, when all sub tasks of Level 2 get completed the connected sub task of Level 1 gets completed. When all the sub tasks of Level 1 get completed, the Main Task get completed.
This feature I have used in MS-Project in very old versions and I am sure there must be a way this could be handled in Jira