How should I bind the "Save as…" option in my application if I have multiple of such options?

I'm writing an application to edit behaviour trees. The application has individual trees, but also a collection of all of the trees in our application. I have a toolbar which has two "Save as..." options: One for saving the whole collection of trees, and one for saving the current tree.

Currently, we have Ctrl+S already reserved for a normal save, and Ctrl+Alt+S reserved for the settings menu.

I can use Ctrl+Shift+S and Ctrl+Shift+Alt+S for both of these options, but I don't think that is the best solution since having to press 4 keys for the "Save as..." option is a bit much.

So my question is: What keyboard shortcuts should I use? What is the best way to bind these to the "Save as..." buttons?