How to have posts in a category as a dropdown on custom menu?

Hi, on my menu I currently have a few pages and some categories that contain my posts. I would like to have all the posts in those categories automatically be a dropdown which is way more convenient then click on the category link and then selecting a post from that page…

I could do it manually by adding a custom link and making it a sub menu to the category but this is rather long and it would be a pain to do this everytime I add new posts, especially since unlike “pages” you can’t have a “display all”