We are aware of the Jira portfolio hierarchy( Theme-> Initiative -> Epic). But can we use any other custom issue type (type is 'standard'), as a parent of EPIC issues? Except initiative issues, can we get any other issues (custom issue type) in the parent link drop down of the EPIC issue?.
No, there is no functionality in Jira for creating new layers of heirarchies.
You should indeed be looking at Advanced Roadmaps (Portfolio) for this, but there are alternatives such as BigPicture, EasyAgile and so-on. If you really explicitly want to do this as an issue type, take a look at Structure though, that does let you emulate more complex hierarchies of types.
Atlassian Marketplace Apps
Unfortunately, Advanced Roadmaps is not available for Jira Server (only Data Center or Cloud Premium or Cloud Enterprise).
Full disclosure, my company's product (Structure) will show up in those search results.
-dave [ALM Works]
Indeed, to get more layers and structurize your task hierarchy better, you will need to look for some apps on the marketplace - such as BigPicture from SoftwarePlant (the company I am part of). With its features, you can organize your task hierarchy in various ways and manage your projects the way you like:
I hope this helps.
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