php problem with php require

i get this errors

Notice: Undefined index: id in D:\xampp\htdocs\menu-class.php on line 3

..... This working only with index.php?id=home on url... i want working and with index.php without ?id= ............any help please?

--------------
index.php

<?php
require 'menu-class.php';
?>
--------------
menu-class.php

<?php

$home = $_GET["id"];

switch($home)
{
case 'home':
require_once 'incls/home.txt';
break;
}

?>