It should first check if the first /$1/ is a directory and if not add a directory before it.
Examples:
1- pizza
2- pizza/olives
Should rewerite the url to:
1- menu/pizza
2- menu/pizza/olives
How is this done?
Options +FollowSymlinks
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^(.*)$ http://mysite.com/menu/$1 [L,QSA]