there are no further levels than Epic - Task - Subtask.
You can construct something similar with links, but this is not the same as a real hierarchy, it's just a link then.
With an app like "Structure" (there may be more, but I know this one) you can create a structural overview (as the name says) with as many hierarchy levels as you want (you have to define them on your own, e.g. with a query), but these levels do exist only in your structure documentation, nowhere else. But maybe this will help you.
Your hierarchy is quite ambiguous in term of implementation. This is my opinion the "conflict" between business vs agile hierarchies.
You have described a business hierarchy, But I guess you want to plan and track its progress, so you need an agile hierarchy for that. And there is some gap in Jira to make those concepts work together with no friction.
In Jira Core, your hierarchy would be built via links. However, Jira Software breaks and transforms the business (core) hierarchy into a plain set of issues (the backlog) and a new hierarchy is built from the ground: Epic -> Story -> Subtask. This is a clean layout very useful to support Agile methodologies (planning and tracking progress). However, it crushes the business point of view of any previous layout.
Links Hierarchy is likely the unique app that combines both concepts seamlessly in Jira: on one hand, it supports business hierarchies and tracking progress on them. On the other hand, it also supports Agile (Jira Software and Portfolio) hierarchies.
IMHO (I work at the Vendor's company) it is worth having a look as you can use issue links to build your hierarchies to describe your business and planning and tracking them directly from Jira Core or use any Atlassian's tool for Agile planning without losing the business perspective.
So answering your question: if you want to "build" a 4th level hierarchy I would recommend do it in Jira with links and use Links Hierarchy to visualize them.
But if you want to plan and track the hierarchy, then you would also need a third-party tool for that: Software or Portfolio. The portfolio supports that 4th level hierarchies but the limitation is that they exist right within the Portfolio environment only. You would still need a tool like Links Hierarchy to extract them from their original environments (Software or Portfolio) and spread them to the rest of Jira (Core), and no-planning users could see them as business hierarchies.
Hope this helps to understand the differences among the hierarchy types and business vs planning layouts to make your decision better regardless of you use our app or not at some time.
