Django: relations between two objects of the same model

Question

I have created this model:

class Process(models.Model):
    name = models.CharField('Process name', max_length=50, unique=True)
    owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.SET_NULL, max_length=50, null=True, verbose_name='Process owner')

I want to create multiple processes and from those build a hierarchy. Here is a hierarchy model:

class Hierarchy(models.Model):
    mainprocess = models.ForeignKey(Process, on_delete=models.CASCADE, related_name='mainprocess', verbose_name='Main process name')
    subprocess = models.ForeignKey(Process, on_delete=models.CASCADE, related_name='subprocess', verbose_name='Sub process name')
    order = models.IntegerField('Process order', default=1)

EDIT: Got it work with code above and now I can build some type of hierarchy, but there are some issues:

• I would like to restrict so that subprocess can be under only one main process. If i create a two different hierarchies with same subprocess it gives an unique contrstraint violation on the subprocess id, so I guess it works now.

• I would like to restrict so that main process and sub process cannot be same. Now I can create it, but is there a way to do this in the model itself or do I restrict this on the client side when hierarchy is created?

What would be the right way to build this type of model/hierarchy? This might be very basic issue, but I couldn't find any related issues to apply a solution from, so any help would be appreciated.

EDIT: what i want to accomplish with the hierarchy model is to keep track on the process tree like for example:

1 Process (main process)
    1.1 process (sub process)
        1.1.1 process (sub process)
    1.2 process (sub process)
        1.2.1 process (sub process)

2 Process (main process)
    2.1 process (sub process)
    2.2 process (sub process)

n Process (main process)
    n.1 process (sub process)
        n.1.1 process (sub process)
            n.1.1.1 process (sub process)
    n.2 process (sub process)