Why tests in Java each time goes faster?

I have a little question about Java optimization. I have a code:

import java.util.LinkedList;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        int testCount = 1_000_000;

        test(testCount);
        test(testCount);
        test(testCount);
    }

    public static void test(int test) {
        List list = new LinkedList();
        long start = System.currentTimeMillis();
        for (int i = 0; i< test; i++) {
            list.add(0, i);
        }
        long finish = System.currentTimeMillis();
        System.out.println("time  " + (finish-start));
    }
}

Each next iteration of this test much less than previous.

time  2443 
time  924
time  143

Could you help me to understand why does it happen?