If you want visitors to trust your website, use the Thawte WebServer Extended Validation certificate.
Issuing these certificates requires thorough data verification. Green color is shown in the address bar to indicate that a valid EV certificate was received.
If you order a certificate for a domain with the www prefix, it will also secure the domain without the www prefix. To do that, you need to specify the domain with the www prefix when generating a certificate signing request (CSR). This rule only applies to third-level domains as www.domain.ru.