vertical menu

Hello,

Does anyone have tips on how to include a vertical kind of menu, like is shown on the website below (for every month)?
https://www.selectiveasia.com/thailand-holidays/weather

I have been searching for a long time already, but I don’t really know how it’s called. I want to include this on a lot of pages, with different kinds of links behind it, so I think I can’t just use a widget for it, can I?

Thanks a lot for your help!!