change the code method into TreeSet .

Sure, here's an example of how to change a Java code that uses a HashSet to use a TreeSet instead:

import java.util.*;

public class Example {
    public static void main(String[] args) {
        // Create a HashSet
        Set<String> hashSet = new HashSet<>();

        // Add some elements
        hashSet.add("apple");
        hashSet.add("banana");
        hashSet.add("orange");

        // Print the HashSet
        System.out.println("HashSet: " + hashSet);

        // Create a TreeSet
        Set<String> treeSet = new TreeSet<>();

        // Add the elements from the HashSet to the TreeSet
        treeSet.addAll(hashSet);

        // Print the TreeSet
        System.out.println("TreeSet: " + treeSet);
    }
}

In this example, we first create a HashSet and add some elements to it. Then, we create a TreeSet and add the elements from the HashSet to the TreeSet using the `addAll` method. Finally, we print out both the HashSet and TreeSet to compare them.

Note that the elements in the TreeSet will be sorted in ascending order, whereas the elements in the HashSet are not guaranteed to be in any particular order.