Weebly currently doesn’t allow you to add a split or a secondary menu bar to a website.
However, you can manually do this if you really want to, by setting up a side column using the multi column tool where you can manually insert text and hyperlinking them to the relevant pages.
This is a bit of a manual process, but you just have to set it up once.
If you need to repeat the process across multiple pages, just highlight the elements (for the secondary menu bar) you have already set up, then “copy” them across to all your pages. This will save you a lot of time from re-creating the same secondary menu bar.