add categories to your custom post type in wordpress (post type here is 'event')

functions.php

	require_once 'post-types/event.php';
	// WP Menu Categories
	add_action( 'init', 'build_taxonomies', 0 );

	function build_taxonomies() {
		register_taxonomy( 'category', 'event', array(
			'hierarchical' => true,
			'label'        => 'Categorieën',
			'query_var'    => true,
			'rewrite'      => true
		) );
	}