Why is it so that java don’t give compile time error when inserting objects in Tree based collections.

It does gives runtime exception. But wouldn’t it be great if it gives compile error.

Code :

import java.util.*;


class Dog{
    int size;
    Dog(int s){
        size = s;
    }

}


public class Test01 {
    public static void main(String[] args) {
        TreeSet set = new TreeSet();
        set.add(new Dog(1));
        set.add(new Dog(2));
        set.add(new Dog(3));
    }
}

It compiles perfect. On runtime it gives ClassCastException complaining that Dog cannot be cast to java.lang.Comparable