Current State:

Currently, Jira Service Management Premium does not support the ability to define or customize work type hierarchies in the same way as Jira Software Premium. Introducing a configurable work type hierarchy would allow organizations to break down and organize service work at multiple levels.
 

Proposed Future State:

Please add support for custom work type hierarchy configuration in Jira Service Management Premium, including the ability to add, rename, and reorder hierarchy levels, and to associate custom work types with each level.