WooCommerce product categories hierarchy (in array).

woo-categories-arr.php

<?php

function get_woocats_arr( $parent = 0, $hierarchy = array() ) {

    $categories = get_terms(
        array(
            'taxonomy' => 'product_cat',
            'orderby'  => 'count',
            'child_of' => $parent,
        ) 
    );

    foreach ( $categories as $category ) {

         if ( 0 === $category->parent ) {

            $hierarchy[ $category->term_id ] = array(
                'slug' => $category->slug, 
                'name' => $category->name, 
                'children' => array(),
            );

            get_woocats_arr( $category->term_id, $hierarchy );

         } else {

            $hierarchy[ $category->parent ]['children'][] = array(
                'slug' => $category->slug, 
                'name' => $category->name, 
                'children' => array(),
            );
         }
    }

    return $hierarchy;
}