How to add nested photo galleries?

Question

Android

I must say right away that I am completely new in Java, I am also self-taught in OOP, so I ask you to specify and at least chew on the answers a little.
Bottom line: I made a photo gallery using this example .
Here is my modified Main.java file . With the help of the volley library, it downloads the json file, takes the addresses of the pictures from it and builds a gallery from them. Clicking on an image opens it in full screen.
Attention to the question: how can I make two levels of nested galleries with minimal changes in the code? That is, when you click on the picture in Maine, a second-level gallery opens, in it - a third-level gallery, and there are already pictures in it.
Just in case, changes have already been made to json - String identifiers year and girlname (these are photos of girls from beauty contests, identifiers indicate the year of the contest and the girl's name).