3 Level Sub Navigation with Ancestor as header

I’ve found a few posts dealing with things similar to what I need, but I can’t figure out how to separate the page/sub-page and sub-page page’s ancestor out into a section title tag above the sidenav.

Closest has been this post.

Here’s what I need:

an H3 with this top level parent always displayed, then a ul with its children displayed and their children (if any) in nested uls

H3 – Parent Title (and link)
– Child Page
— Sub-child page
— Sub-child page
— Sub-child page
– Child Page
— Sub-child page
— Sub-child page
– Child Page

The issue I’ve been having is getting this navigation to be identical regardless of what page you’re on under there – ancestor to child.

Can anyone help? Thanks!

[please do not bump – rather try to provide more information that might be helpful]