Expandable-RecyclerView/app/src/main/java/com/github/adriankuta/MainActivity.kt

package com.github.adriankuta

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import com.github.adriankuta.databinding.ActivityMainBinding
import com.github.adriankuta.expandable_recyclerview.expandableTree

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val tree = expandableTree(Region("World")) {
            child(Region("North America")) {
                child(Region("USA"))
            }
            child(Region("Europe")) {
                child(Region("Poland")) {
                    child(Region("Warsaw"))
                }
                child(Region("Germany"))
            }
            child(Region("Asia")) {
                child(Region("China"))
            }
        }

        val adapter = ExpandableAdapter()
        binding.recyclerView.adapter = adapter
        adapter.setTree(tree)
    }
}