It’s not obvious how to configure the Trusted Sites list for Internet Explorer 11 via group policy. The GPO settings to configure IE 11 Trusted Sites are here:
User Configuration -> Policies -> Administrative Templates -> Windows Components -> Internet Explorer -> Internet Control Panel -> Security Page
The GPO setting to change is called Site to Zone Assignment List. To configure the list of sites as Trusted Sites, you have to list the website, then give it a value of 2, as per the explanation in the GPO setting.