Class level locking with synchronization block, multiple threads on same instance

I have following code where multiple threads are invoking same instance method which is guarded by static object

package com.data;

class TestThread {

private final static Object object = new Object();

public void myWaitMethod() {
    synchronized (object) {
        System.out.println("Before a " + Thread.currentThread().getId());
        try {
            object.wait();
        } catch (Exception ignore) {
            System.out.println(Thread.currentThread().getId());
        }
        System.out.println("After a " + Thread.currentThread().getId());
    }
}

public void myNotifyMethod() {
    synchronized (object) {
        System.out.println("Before Notify");
        object.notifyAll();
        System.out.println("After b");
    }
}

public static void main(String[] args) throws InterruptedException {
    TestThread aa1 = new TestThread();
    new Thread(() -> aa1.myWaitMethod()).start();
    new Thread(() -> aa1.myWaitMethod()).start();
    Thread.sleep(1000);
    System.out.println("sleep");
    Thread.sleep(1000);
    aa1.myNotifyMethod();
}
}

o/p:

Before a 12
Before a 13
sleep
Before Notify
After b
After a 13
After a 12

I don't understand why "Before a" twice printed even though the block is synchronized.