An alias to a subdomain ? — Plesk

Need a domain alias for a sub-domain?
Plesk had a direct option to do this from the front end, which was
taken out in newer versions of Plesk.

You can configure a .com alias to a subdomain by :
create a file in the subdomains conf directly like this:
# vi /var/www/vhost/

ServerAlias ""
ServerAlias ""

then rebuild apache config like:
# /opt/psa/admin/sbin/httpdmng --reconfigure-all