Find tags in given tag group, list tags and entries under each tag

list_categories_and_entries_craft.twig

{#
 # FIELD_NAME is name of field
 # sampleCategories, sampleCategory, category, entry, entries can be anything
 #}
 
{% set sampleCategories = craft.tags.set('FIELD_NAME') %}
<ul>
    {% for sampleCategory in sampleCategories %}
        {% set category = craft.tags.search('name:'~sampleCategory.name).first() %}
        {% if category %}
        <li>
            <h2>{{ category }}</h2>
            {% set entries = craft.entries.parentOf(category).find() %}
            <ul>
            {% for entry in entries %}
                <li>{{ entry.title }}</li>
            {% endfor %}
            </ul>
        </li>
        {% else %}
            {% exit 404 %}
        {% endif %}
    {% endfor %}
</ul>