pages-taxonomy.php

/**
* Add taxonomy to pages
*/
function bnn_add_pages_tax() {
	register_taxonomy(
		'page_category',
		'page',
		array(
			'label' => __( 'Categories' ),
			'rewrite' => array( 'slug' => 'page-category' ),
			'hierarchical' => true,
			'show_admin_column' => true,
		)
	);
}
add_action( 'init', 'bnn_add_pages_tax' );