Add WordPress admin menu + submenu

functions-class.php

<?php
class WeAreWP {
	
	
	function __construct() {
	}
	
	function init() {
		add_action( 'admin_menu', array( $this, 'wearewp_plugin_top_menu' ) );
	}
	
	function wearewp_plugin_top_menu(){
		add_menu_page( 'WeAre[WP]', 'WeAre[WP]', 'manage_options', 'wearewp', array( $this, 'wearewp_render_plugin_page' ) );
		
		add_submenu_page( 'wearewp', 'About', 'About', 'manage_options', 'wearewp-about', array( $this, 'wearewp_render_about_page' ) );
	}

	function wearewp_render_plugin_page(){
		?>
		<div class='wrap'>
			<h2>Plugin page</h2>
		</div>
		<?php
	}

	function wearewp_render_about_page(){
		?>
		<div class='wrap'>
			<h2>About page</h2>
		</div>
		<?php
	}
}

$wearewp = new WeAreWP();
$wearewp->init();

functions.php

<?php
add_action('admin_menu','wearewp_plugin_top_menu');
function wearewp_plugin_top_menu(){
	add_menu_page( 'WeAre[WP]', 'WeAre[WP]', 'manage_options', 'wearewp', 'wearewp_render_plugin_page' );
	
	add_submenu_page( 'wearewp', 'About', 'About', 'manage_options', 'wearewp-about', 'wearewp_render_about_page');
}

function wearewp_render_plugin_page(){
	?>
	<div class='wrap'>
		<h2>Plugin page</h2>
	</div>
	<?php
}

function wearewp_render_about_page(){
	?>
	<div class='wrap'>
		<h2>About page</h2>
	</div>
	<?php
}

Cool !
Merci pour la function !