List posts under category and subcategories

I am looking to list the posts on my archive page as follows:

Main Category
– Sub Category
— Sub Category Products
– Sub Category
— Sub Category Products
– Remaining Main Category Products

I am using a custom taxonomy and post type. As of right now I have this:

$term_children = get_terms('product_category', array( 'parent' => get_queried_object_id(), ) );

            if (! is_wp_error($terms)){
                foreach ($term_children as $child){
                    echo '<h3>' . $child->name . '</h3>';
                    $term_grandchildren = get_terms('product_category', array('parent' => $child->term_id,));
                    if(! is_wp_error($terms)){
                        foreach ($term_grandchildren as $gchild){
                            echo '<h4>' . $gchild->name . '</h4>';
                            $query_args['tax_query'] = array(
                           array(
                               'taxonomy' => $gchild->taxonomy,
                               'terms'    => (int)$gchild->term_id,
                               'field'    => $gchild->slug,
                               ),
                            );
                            $products = new WP_Query( $query_args );
                            while ( $products->have_posts() ) : $products->the_post();
                                ?>
                                <a href="<?php the_permalink();?>"><?php the_title();?></a><?php
                            endwhile;
                        }
                    }
                }
            }

But I’m not sure if this is correct and I’m also not sure how to grab the remaining products that are part of the main category.