Twig HTML Select Macro with optgroups

macros.twig

{% macro select (name, id, options, selected, required, includeBlank) %}
    <select name="{{ name }}" id="{{ id }}" {{ required ? 'required' : '' }}>
        {% if includeBlank %}
            <option value=""></option>
        {% endif %}
        {% for key, value in options %}
            {% if value is iterable %}
                <optgroup label="{{ key }}">
                    {% for subKey, subValue in value %}
                        <option value="{{ subKey }}" {{ subKey == selected ? 'selected' : '' }}>{{ subValue }}</option>
                    {% endfor %}
                </optgroup>
            {% else %}
                <option value="{{ key }}" {{ key == selected ? 'selected' : '' }}>{{ value }}</option>
            {% endif %}
        {% endfor %}
    </select>
{% endmacro %}

{% set groups = {
    'Optgroup A': {
        'A': 'Super Super',
        'B': 'Super',
        'C': 'Power',
        'D': 'Regular',
        'E': 'Guest'
    },
    'Optgroup B': {
        'ASDF': 'Super Admin',
        'ZXCV': 'Power User',
        'QWER': 'ZXCV 123'
    }
} %}
{{ macros.select('group', 'group', groups, user.group, true, true) }}