[Answered ]-Django admin: reverse select foreign keys

For you requirement, you can use ManyToManyField in Bundle model instead of ForeignKey in Product model.
Check below code.

class Bundle(models.Model):
    title = models.CharField(max_length=255)
    product = models.ManyToManyField('Product')


class Product(models.Model):
    title = models.CharField(max_length=255)

Then you can register admin interfaces:

admin.site.register(Bundle)
admin.site.register(Product)

Then you can add series of Product from a dropdown/search.