foundry/Data/systems/dnd5e/templates/apps/parts/trait-list.hbs

<ol class="trait-list">
  {{#each choices as |choice key|}}
    <li>
      <label class="checkbox">
        <input type="checkbox" name="{{#if ../prefix}}{{../prefix}}.{{/if}}{{key}}" {{checked choice.chosen}}>
        {{choice.label}}
      </label>
      {{#if choice.children}}
        {{> "dnd5e.trait-list" choices=choice.children prefix=../prefix}}
      {{/if}}
    </li>
  {{/each}}
</ol>