Linq union on anonymous types

Recently in my project, i was trying to do a LINQ union on two anonymous types. The compiler didn't seem to be happy with it. Here is what i was trying to do:

var query = (from t in taskRepository
                         join s in stepRepository on t.TaskID equals s.ID
                         where t.UserID == 420
                         select new{ID = t.ID,DisplayText = t.DisplayText,ReviewStepID = null
                         })
                       .Union
                       (from rs in reviewStepsRepository
                        where rs.ReviewTypeID == 2
                        select new{ID = null,DisplayText = rs.ReviewName,ReviewStepID = rs.ID
                        })
                       .OrderByDescending(o => o.ID);

With some research, ended up creating a class with ID,DisplayText and ReviewStepID

 public class MyTask
          {
                public int? ID { get; set; }
                             public string DisplayText { get; set; }
                             public int? ReviewStepID { get; set; }
           }

And, the happy LINQ query looked like below:

var query = (from t in taskRepository
                     join s in stepRepository on t.TaskID equals s.ID
                     where t.UserID == 420
                     select new MyTask() { ID = t.ID,                                            
                                          DisplayText = t.DisplayText,
                                          ReviewStepID = null  
                                       }) .Union 
                                         (from rs in reviewStepsRepository
                                          where rs.ReviewTypeID == 2
                                          select new MyTask() { ID = null, 
                                                                DisplayText = rs.ReviewName, 
                                                                ReviewStepID = rs.ID })
                        .OrderByDescending(o=>o.ID); 

Happy LINQ'ING!!!