How to check if model has something inside in django?

I have a model of Branch, and a model of Worker. I want to filter only these branches, which have at least one user inside.

models.py

class Branch(models.Model):
    name = models.CharField(max_length=100)

class Worker(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    fullname = models.CharField(max_length=150)
    branch = models.ForeignKey(Branch, on_delete=models.SET_NULL, null=True, related_name='branch')
    position = models.CharField(max_length=200)
    manager = models.BooleanField(default=False)

I tried to add related_name to worker-branch, but now I don't know how to use it, and is it right way to do so?
I also tried to filter like that: Worker.objects.filter(branch=?).exists(). But it doesn't make sense.

At the end I want to have a list of branches which have at least one worker.

Try this and let me know if it helps, it should work, not sure though:

Branch.objects.filter(branch__isnull=False)

Not elegant at all, but you could also use Count and queryset annotation. Also, "branch" is a terrible name for a set of users assigned to a branch, so the related name should be "users" or "assigned_users" or so.

EDIT:

Branch.objects.filter(branch__isnull=False).distinct()

to get rid of duplicates

I prefer the following approach (easier to read):

Branch.objects.exclude(branch__isnull=True)