parameters in url is automatically deleted in wordpress

Question

I built a custom plugin on which I get the value of parameter to validate my page,
Here is my sample code:

www.test.com/user/?page="Parameter"

 <?php if(empty($_REQUEST['page'])) { ?>
Landing Page
 <?php }else if( $_REQUEST['page'] == 'add_User'){ ?>
Add User
   <?php }else if( $_REQUEST['page'] == 'edit_User'){
Edit User
<?php } ?>

But my problem is wordpress automatically removes the page="Parameter part" .

Answer 1

"?page" is a reserved word that is why it is automatically culled.