A TreeSet built from a list with repeats

import java.util.*;

public class Main {
    public static void main(String[] args) {
        TreeSet<Integer> set = new TreeSet<>(List.of(5, 1, 3, 1, 5));
        System.out.println(set);
        System.out.println(set.first() + " " + set.last());
        System.out.println(set.headSet(3));
    }
}