code: def get_all_related_companies(self, include_self=False):
          
          parents = self.get_all_parents()
          subsidiaries = self.get_all_children()
          related_companies = parents | subsidiaries
  
          if include_self is True:
              company_qs = Company.objects.filter(id=self.id)
              related_companies = related_companies | company_qs
  
          related_companies_ids = [company.id for company in list(set(related_companies))]
          related_companies = Company.objects.filter(id__in=related_companies_ids)
  
          return related_companies
docs: Return all parents and subsidiaries of the company
          Include the company if include_self = True