function woo_add_custom_general_fields() {

    echo '<div class="options_group">';

$users = get_users( array( 'fields' => array( 'ID' ) ) );
foreach($users as $key => $term){
      $options[$term] = $term;
    }

  woocommerce_wp_select( array(
      'id' => '_select',
      'label' => __( 'Custom Select Field', 'boipoka' ),
      'options' => $options
          )
          );
    echo '</div>';
}
add_action( 'woocommerce_product_options_general_product_data','woo_add_custom_general_fields' );