{% for department in form.departments %}
{% with deptid=department.instance.id|stringformat:"s"|default:'new' %}
{% with collapse_id="collapse-department-"|add:deptid %}
{% bootstrap_form department %}
{{ department.units.management_form }}
{{ department.units.non_form_errors }}
Units
{% for unit in department.units.forms %}
{% with unitid=unit.instance.id|stringformat:"s"|default:'new' %}
{% with unit_collapse_id="collapse-department-"|add:deptid|add:"-"|add:unitid %}
{{ unit.management_form }}
{{ unit.non_form_errors }}
{% bootstrap_form unit %}