Drupal 8: Commerce condition form element.

example_commerce_conditions.php

<?php
/**
 * Implements hook_form_alter().
 */
function HOOK_form_alter(&$form, FormStateInterface $form_state, $form_id) {
  if (in_array($form_id, ['commerce_tax_type_edit_form', 'commerce_tax_type_add_form'])) {
    $form['commerce_conditions'] = [
      '#type' => 'commerce_conditions',
      '#title' => t('Conditions'),
      '#default_value' => [],
      '#parent_entity_type' => 'commerce_tax_type',
      '#entity_types' => ['commerce_order_item'],
    ];
  }
}