Java记录 -60- TreeSet抛出ClassCastException

public class TreeSetTest {
public static void main(String[] args){
TreeSet tree = new TreeSet();
tree.add(new Pepole("zhangsan"));
tree.add(new Pepole("lisi"));

System.out.println(tree);
}
}
class Pepole{
int age;
String name;
public Pepole(String name){
this.name = name;
}
}

Exception in thread "main" java.lang.ClassCastException: my.set.Pepole cannot be cast to java.lang.Comparable
at java.util.TreeMap.put(TreeMap.java:542)
at java.util.TreeSet.add(TreeSet.java:238)
at my.set.TreeSetTest.main(TreeSetTest.java:10)

ClassCastException