add menu item under custom post type code example

Example: hide category menu from custom post type

<?php

function by_remove_menu_pages() {
	// remove testimonials menu section
	// remove_menu_page( 'edit.php?post_type=testimonials-widget' );
	// remove categories
	remove_submenu_page( 'edit.php?post_type=testimonials-widget', 'edit-tags.php?taxonomy=category&amp;post_type=testimonials-widget' );
	// remove tags
	remove_submenu_page( 'edit.php?post_type=testimonials-widget', 'edit-tags.php?taxonomy=post_tag&amp;post_type=testimonials-widget' );
	// remove settings
	remove_submenu_page( 'edit.php?post_type=testimonials-widget', 'testimonialswidget_settings' );
}

add_action( 'admin_menu', 'by_remove_menu_pages', 999 );