public void Sync()
{
var itemsMissingInOutlook = GetMissingAppointments(sourceCalendar: _googleCalendarService, destinationCalendar: _outlookCalendarService).ToList();
var itemsMissingInGoogle = GetMissingAppointments(sourceCalendar: _outlookCalendarService, destinationCalendar: _googleCalendarService).ToList();
_outlookCalendarService.AddItems(itemsMissingInOutlook);
_googleCalendarService.AddItems(itemsMissingInGoogle);
}