Craft CMS. Categories tree

categories.twig

<div>
    {% for category in craft.categories.all() %}
        {% if category.level == 1 %}
            {% set children = category.getChildren() %}

            <h4>{{ category.title }}</h4>
            {% if children|length %}
                <ul>
                    {% for subcategory in children %}
                        <li>{{ subcategory.title }}</li>
                    {% endfor %}
                </ul>
            {% endif %}
        {% endif %}
    {% endfor %}
</div>