class LB(models.Model):
    name = models.CharField('Имя (hostname)', max_length=128, unique=True)
    ip_address = models.CharField('Management IP', max_length=128, default=False)
    port = models.PositiveIntegerField('Management port', default=50051)
    description = models.CharField('Описание', max_length=256, null=True)
    lb_units = models.ManyToManyField(
            LBU,
            through='BalancerUnits',
            through_fields=('lb', 'lbu')
    )
    def save(self, *args, **kwargs):
        super(LB, self).save(*args, **kwargs)
        save_tree()
def save_tree():
    all_lb = LB.objects.all()
    all_bu = BalancerUnits.objects.all()
    all_lbureals = LBUReal.objects.all()
# ... calculating tree