How to create tabs inside tabs

[marcell]

I followed this tutorial https://www.w3schools.com/howto/howto_js_tabs.asp and it's working but how do I put subtabs inside the main tabs? For example, main tabs are tab 1, tab 2 and tab 3. I want to put sub tabs 4 and 5 inside tab 1, in a way that when you click tab 4 or 5 both of them stil stay appearing like the main ones, instead of disappearing if you click on one of them. I hope I'm not being confusing.