Ask God for advice, why can only 5 pieces of data be added to treeMap?

 1  @org.junit.Test
 2     public void TestTreeMap2(){
 3         Comparator comparator=new Comparator() {
 4             @Override
 5             public int compare(Object o1, Object o2) {
 6                 if (o1 instanceof Student && o2 instanceof Student){
 7                     Student stu1=(Student)o1;
 8                     Student stu2=(Student)o2;
 9                     int i=stu1.getName().compareTo(stu2.getName());
10                     if(i==0){
11                         return stu1.getAge().compareTo(stu1.getAge());
12                     }
13                     return i;
14                 }
15                 return 0;
16             }
17         };
18 
19 
20         Map<Student,Integer> treeMap = new TreeMap<>(comparator);
21         treeMap.put(new Student("aaa",12), 12);
22         treeMap.put(new Student("xxx",15), 56);
23         treeMap.put(new Student("fff",14), 111);
24         treeMap.put(new Student("hhh",15), 12);
25         treeMap.put(new Student("bbb",21), 89);
26         treeMap.put(new Student("bbb",19), 15);
27 
28         Set entry=treeMap.entrySet();
29         for (Object obj:entry){
30             Map.Entry e=(Map.Entry)obj;
31             System.out.println(e);
32         }
33 
34 
35     }