Subtask of a Subtask (sub-sub-task)

This request has come from my project management users on several occasions and I have not found a similar request in this database.

The Background =
Project Managers are required to have a corresponding JIRA number for each task within their project plans within my client site.
Of course, they are using MS Project and their project plans are much like:
Task

• Sub Task
  • Sub Sub Task
  • Sub Sub Task
• Sub Task
  • Sub Sub Task

My users want to be able to completely match this structure within their JIRA projects so when they pull up a main task, the subsequent sub tasks and sub-sub tasks appear under the issue.