product-registration.php

<?php

$product_meta_box = new_cmb2_box( array(
	'id'            => 'product_meta_box',
	'title'         => __( 'Product Details', 'sample' ),
	'object_types'  => array( 'product' ),
	'context'       => 'normal',
	'priority'      => 'high',
	'show_names'    => true,
) );

$product_meta_box->add_field( array(
	'name'    => __( 'Subheader', 'sample' ),
	'id'      => 'product-subheader',
	'type'    => 'text',
) );

$case_study_options = array();
$cast_studies = array(
	'1' => 'Rad Case Study',
	'2' => 'Wicked Case Study',
	'3' => 'Cool Case Study',
);
$case_study_options['add_row_text'] = __( 'Add Case Study', 'sample' ); // Ruh Roh
$product_meta_box->add_field( array(
	'name'             => __( 'Case Study', 'sample' ),
	'id'               => 'prouct-case-study',
	'type'             => 'select',
	'show_option_none' => true,
	'repeatable'       => true,
	'options'          => $case_study_options,
) );