Django - How to create many to one relation

In my application there is many-to-one relation, such as one teacher can teach more than one subject. So in admin panel I can't simulate it. Can't add more than one subject:

Here are my codes:

models.py:

class Subject(models.Model):
    def __str__(self):
        return self.name

    name = models.CharField(max_length=200)
    credit = models.IntegerField()

class Teacher(models.Model):
    def __str__(self):
        return self.name

    name = models.CharField(max_length=100)
    email = models.CharField(max_length=100, null=True)
    chair = models.ForeignKey(Chair, on_delete=models.CASCADE)
    academic_degree = models.CharField(max_length=100)
    subject = models.ForeignKey(Subject, on_delete=models.CASCADE)