### Summary The limit for nesting of Epic is supposed to be 7 (https://gitlab.com/gitlab-org/gitlab/blob/60578471549081ca980ec5cc961b35ea1d9a6e65/ee/app/models/ee/epic.rb#L154). However, this is inconsistently applied, and in some cases the effective limit is one less (6) With an existing 6-level-deep epic structure, it is possible to add a 7th-level child epic to one that is 6 levels deep using the "Add" dropdown on the right of the epic structure panel , choosing "Add a new epic". However, adding an *existing* epic either by using: 1. "Add an existing Epic" from the "Add" dropdown, or 2. The `/parent_epic` quick command when creating an epic via the "New Epic" web interface will fail with message that "This epic cannot be added. One or more epics would exceed the maximum depth (7) from its most distant ancestor.". ### Steps to reproduce * Create 6 levels of nested epics * Add a 7th level using "Add a new epic"'; it will succeed * Create a new epic (top level, no parent) directly * Use "Add an existing Epic" to try to add this separate epic as a child to the 6th level epic; it will fail with the above noted error message * Or, in the separate epic try to use `/parent_epic` to add it to the 6th level epic; it will fail with *no* error message; the flash claims it worked, but it has silently failed. ### Example Project ### What is the current *bug* behavior? Cannot add a 7th level epic to a nested structure when using 'add an existing epic' ### What is the expected *correct* behavior? You should be able to add the 7th level epic, as it is possible via other paths. ### Relevant logs and/or screenshots This can be seen (a test group of mine in staging):  where I added `Level 7 (3)` with "Add a new epic", but cannot add Epic `&10` using "Add an existing Epic" ### Output of checks This bug happens on GitLab.com, but is not specific to .com ### Possible fixes https://gitlab.com/gitlab-org/gitlab/blob/60578471549081ca980ec5cc961b35ea1d9a6e65/ee/app/models/ee/epic.rb#L431 and https://gitlab.com/gitlab-org/gitlab/blob/60578471549081ca980ec5cc961b35ea1d9a6e65/ee/app/models/ee/epic.rb#L515 seem to be implementing similar checks, and https://gitlab.com/gitlab-org/gitlab/blob/60578471549081ca980ec5cc961b35ea1d9a6e65/ee/app/models/ee/epic.rb#L492 and https://gitlab.com/gitlab-org/gitlab/-/blob/60578471549081ca980ec5cc961b35ea1d9a6e65/ee/app/services/epic_links/create_service.rb#L11 generate the same error message So it seems that one of those checks is wrong and there's an opportunity to tidy this code up so there's less duplication and consistent behavior.