How to close the level, and to open it, you need to go through the previous level?

Question

Unity

I created just such a level map
How to close simple levels (image does not help) and in order to open them, you need to go through the previous level? so how to implement it? I did not find tutorials on this topic through the UI.

Answer 1

www.thegamecontriver.com/2014/09/create-level-lock...
Okay, I found it in English, but you can figure it out.

Answer 2

and userDefaults store the maximum open level. default open first