Modeling Employee-Assistant(s) relationship with EF Code First

Here are the business requirements, in short:

• All employees need to be stored in a database
• Some employees have assistants, some do not
• Some employees have more than one assistant
• Assistants are employees, as well

There is obviously a bit of a self-referencing situation. But the difference from a typical "Employee-Manager" situation is that here one Employee can have 0 or multiple assistants. So, the combination of Employee and employee's Assistants needs to be stored in a separate table in a one-to-many relationship between Employee and EmployeeAssistant. But I'm getting confused how to model this in Entity Framework 6 Code First.

I started with this:

public class Employee
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

public class EmployeeAssistant
{
   [ForeignKey("Employee")]
   public int EmployeeId { get; set; }
   public virtual Employee Employee { get; set; }

   [ForeignKey("Assistant")]
   public int AssistantId { get; set; }
   public virtual Employee Assistant { get; set; }
}

But I get an error during Update-Database command:

Introducing FOREIGN KEY constraint 'FK_dbo.EmployeeAssistant_dbo.Employee_EmployeeId' on table 'EmployeeAssistant' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.

What am I missing? Should I approach this differently?