Hide field when parent.level is lower then 5?

Question

How can i hide a field "content", when parent level is lower then 5 in mptt.django ? I want edit a field when descendent is 5.

class Menu(MPTTModel):
name = models.CharField(max_length=50, blank=True, null=True)
content = models.TextField(verbose_name='content')
parent = TreeForeignKey('self', null=True, blank=True, related_name='children')

def __str__(self):
    return self.name

forms.py

class BookAdmin(admin.ModelAdmin):

def get_form(self, request, obj=None, **kwargs):
    if parent and parent.level <= 5:
        self.exclude = ("content", )

i want create somethink of that