Easy Digital Downloads Function: edd_is_download_in_bundle used to determine if a download is included in a specific bundle.

edd_is_download_in_bundle.php

<?php

/**
 * Determines if a download is included in a specific bundle. 
 * 
 * @param $download_id
 * @param $bundle_id
 *
 * @return bool
 */
function edd_is_download_in_bundle( $download_id, $bundle_id ) {
	$bundled_products = edd_get_bundled_products( $bundle_id );
	return in_array( $download_id, $bundled_products );
}