Display multiple selected checkboxes ticked in update form in django

In my create form i have saved certain values of season_interest as summer, winter in my database

now these values should be shown ticked in update form

let us consider my forms.py as

        SEASON_INTEREST_CHOICES = (
                ('Spring','Spring'),
                ('Summer','Summer'),
                ('Autumn','Autumn'),
                ('Winter','Winter'),
                ('Year round','Year round'),
            )

class HorticlutureUpdateForm(BetterModelForm):
        season_interest = forms.MultipleChoiceField(
                    required=False,label=('Season of Interest'),
                    widget=forms.CheckboxSelectMultiple(attrs={'checked' : 'checked'}),
                    choices=SEASON_INTEREST_CHOICES,
                )

here is my models.py

class Items(models.Model):
   SEASON_INTEREST_CHOICES = (
        ('Spring','Spring'),
        ('Summer','Summer'),
        ('Autumn','Autumn'),
        ('Winter','Winter'),
        ('Year round','Year round'),
    )
   season_interest = models.CharField(max_length=200,blank=True, null=True,verbose_name='Season of Interest')

When i am using widget=forms.CheckboxSelectMultiple(attrs={'checked' : 'checked'}) in updateform it is showing all the choices as ticked rather than the values that are saved in database(i.e clay, chalk only should be ticked in updateform display)

Currently it is showing in this way in update form