loop.php

<?php $subCategories = get_term_children($queried_object->term_id, 'product_cat') ?>
<?php if($queried_object->post_type == 'page'): $categories = get_terms('product_cat'); ?>

  <?php foreach($categories as $category): ?>
    <?php if($category->count && ($category->parent == 0)): ?>
      <h4><?php echo $category->name ?></h4>
      <?php echo do_shortcode('[product_category category="' . $category->slug . '"]'); ?>
    <?php endif; ?>
  <?php endforeach; ?>

<?php elseif(count($subCategories)): ?>

  <?php foreach($subCategories as $subCategory): $subTerm = get_term_by( 'id', $subCategory, 'product_cat' ); ?>
    <?php if($subTerm->count): ?>
      <h4><?php echo $subTerm->name ?></h4>
      <?php echo do_shortcode('[product_category category="' . $subTerm->slug . '"]'); ?>
    <?php endif; ?>
  <?php endforeach; ?>

<?php else: ?>
  <?php woocommerce_product_loop_start(); ?>
  <?php woocommerce_product_subcategories(); ?>
  <?php while ( have_posts() ) : the_post(); ?>
    <?php wc_get_template_part( 'content', 'product' ); ?>
  <?php endwhile; // end of the loop. ?>
  <?php woocommerce_product_loop_end(); ?>
  <?php do_action( 'woocommerce_after_shop_loop' ); ?>
<?php endif; ?>