Codeigniter htaccess只在根目录下重定向到index.php

I have structure directory in Codeigniter like this

/application
/assets
/system
.htaccess
index.php
test.php

And this is my .htaccess file

RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule .* index.php/$0 [PT,L]

What i want is, if user access any other PHP or HTML file except index.php, it'll be redirected to index.php. For example, if someone access test.php, it'll be redirected to index.php. But i want it only work for root directory and not effected to other directory

I've already try from here but it didn't work for me