Django如何构建QuerySet实现多层级关联对象分组并渲染模板

在模板中按指定层级结构展示计划数据，目标展示结构如下：

PLan 1: ABC
 - General Objective 1
     - Sub-Objective-1
       - Task 1
       - Task 2
     - Sub-Objective-2
       - Task 1
PLan 2: ZZZ
 - General Objetivo General 1
     - Sub-Objetivo-1
       - Tarea 1
PLan 3: DDD
 - General Objetivo General 1
     - Sub-Objetivo-1
       - Tarea 1
     - Sub-Objetivo-2
       - Tarea 1

• 1个ActionPlan（计划）可包含多个PlanObjective（总目标）
• 1个PlanObjective（总目标）可包含多个PlanSubObjective（子目标）
• 1个PlanSubObjective（子目标）可关联多个PlanSubObjectiveTask（任务）

class PlanObjective(models.Model):
    actionplan = models.ForeignKey(ActionPlan, on_delete=models.CASCADE)
    center = models.ForeignKey(Center, on_delete=models.CASCADE)
    centerobjective = models.ForeignKey(CenterObjective, null=True, on_delete=models.SET_NULL)
    description = models.TextField(max_length=250, null=False, default='')

class PlanSubObjective (models.Model):
    actionplan = models.ForeignKey(ActionPlan, on_delete=models.CASCADE)
    center = models.ForeignKey(Center, on_delete=models.CASCADE)
    planobjective = models.ForeignKey(PlanObjective, on_delete=models.CASCADE)
    description = models.TextField(max_length=250, null=False, default='')


class PlanSubObjectiveTask (models.Model):
    actionplan = models.ForeignKey(ActionPlan, on_delete=models.CASCADE)
    center = models.ForeignKey(Center, on_delete=models.CASCADE)
    planobjective = models.ForeignKey(PlanObjective, on_delete=models.CASCADE)
    plansubobjective = models.ForeignKey(PlanSubObjective, on_delete=models.CASCADE)
    is_complete = models.CharField(max_length=2, null=True, blank=True, default='0')

现有查询语句从任务表出发查询：

plans = PlanSubObjectiveTask.objects.filter(period=period).select_related(
        'plansubobjective', 'planobjective', 'actionplan')

尝试使用Django内置的regroup模板标签实现多层分组，但未得到预期效果，需要更合理的QuerySet构建方案实现上述层级数据展示。

内容的提问来源于stack exchange，提问作者Gully