Board Thread:Support Requests - Getting Technical/@comment-4059391-20161017193737/@comment-27345308-20161017194131

You might want to read this section of the navigation bar help page. You can only have 4 Level 1, 7 Level 2 and 10 Level 3 links.

However, I think there might be scripts on Dev Wiki (ExtendedNavigation adds Level 4 and 5 links, for example) that could do that, and if there aren't, you could make it yourself or ask somebody to make it in JavaScript.