Django Model Form field data not displaying - django

Question

So I am trying to figure out why my dropdown menu will not display the list of collections for the user to pick from.
Form Screenshot: [1]: https://i.stack.imgur.com/UIrq6.png
Here is the Form.py file class used for this problem:
class ProductForm(ModelForm):
class Meta:
model = listing
fields = 'all'
_---------------------------------------------
Here is the user form VIEW:
def index(request):
form = ProductForm
if request.method == 'POST':
form = ProductForm(request.POST)
if form.is_valid():
form.save()
context = {'form':form}
return render(request, 'index.html', context)
Here is also the code for the 2 models here:
class Collection(models.Model):
title = models.CharField(max_length=255)
def __str__(self) -> str:
return self.title
class Meta:
ordering = ['title']
class listing(models.Model):
image = models.ImageField(blank=True, null=True)
name = models.CharField(max_length=255)
description = models.TextField()
unit_price = models.DecimalField(max_digits=6, decimal_places=2, validators=[MinValueValidator(1)])
inventory = models.IntegerField()
last_update = models.DateTimeField(auto_now=True)
collection = models.ForeignKey(Collection, on_delete=models.PROTECT, blank=True, null=True)
vendors = models.ForeignKey(User, on_delete=models.CASCADE, null=True, blank=False)
I'm somewhat new to django and just trying to understand why for the form it won't display the list of collections in the dropdown.