Difference between ApplicationInstance.Start(ServerManager) and ServerManager.Start(ApplicationInstance)

Question

I'm trying to understand the code I have derived and I am confused through call of two methods by start of OPC-UA server. I'm using Unified Automation implementation of OPC-UA.

First called

UnifiedAutomation.UaBase.ApplicationInstance.Start(ServerManager,,)

then called

UnifiedAutomation.UaServer.ServerManager.Start(ApplicationInstance)

Here is abstracted code:

var application = new ApplicationInstance();
var serverManager = new ServerManager("companiURI", "applicationName");
...
application.Start(serverManager, p=>{}, null)
if (!Environment.UserInteractive)
{
    serverManager.Start(application);
}

So what is the difference between these two methods?