// Register the Tab by hooking into the 'woocommerce_product_data_tabs' filter
add_filter( 'woocommerce_product_tabs', 'add_my_custom_product_data_tab' );
function add_my_custom_product_data_tab( $product_data_tabs ) {
    $product_data_tabs['my-custom-tab'] = array(
        'label' => __( 'My Custom Tab', 'my_text_domain' ),
        'target' => 'my_custom_product_data',
    );
    return $product_data_tabs;
}

// tab content hooking into the 'woocommerce_product_data_panels' action hook

add_action( 'woocommerce_product_data_panels', 'add_my_custom_product_data_fields' );
function add_mailchimp_product_data_fields() {
    global $woocommerce, $post;
    ?>
    <div id="my_custom_product_data" class="panel woocommerce_options_panel">
        <?php
        woocommerce_wp_checkbox( array(
            'id'            => '_my_custom_field',
            'wrapper_class' => 'show_if_simple',
            'label'         => __( 'My Custom Field Label', 'my_text_domain' ),
            'description'   => __( 'My Custom Field Description', 'my_text_domain' ),
            'default'       => '0',
            'desc_tip'      => false,
        ) );
        ?>
    </div>
    <?php
}