Wild card SSL and sub domain website

If you have a SSL certificate for your site, is it necessary to have a second SSL certificate (like a wild card SSL) for a subdomain ?

A wildcard covers one level, for example :


However you can have multiple subdomain names with a same certificate.

For a subdomain of a subdomain, you need another wildcard SSL certificate. You can also buy a multi-domain wildcard certificate that can secure up to one hundred of websites and unlimited sub-domains.