Developer.cs

public class Developer : IdentityEntity
{
    public string Name { get; set; }

    public DevType DevType { get; set; }

    private ICollection<TaskToDo> _tasksToDo { get; set; }        
    public virtual IReadOnlyCollection<TaskToDo> TasksToDo { get { return _tasksToDo as Collection<TaskToDo>; } }

    public Developer()
    {
        _tasksToDo = new Collection<TaskToDo>();
    }

    public void AddItemToDo(TaskToDo todo)
    {
        var _todo = new TaskToDo() {
            Start = todo.Start,
            DeadLine = todo.DeadLine,
            Title = todo.Title,
            Status = todo.Status,
            Id = this.Id
        };
        _tasksToDo.Add(_todo);
    }
}