DataContract not available at WCF client service reference

DataContract not available at WCF client service reference

I have this Data contract in my WCF service
[DataContract]
public class Department
{
[DataMember]
public List<Section> Sections { get; set; }
}
[DataContract]
public class Section
{
[DataMember]
public List<Room> Rooms { get; set; }
}
[DataContract]
public class Room
{
[DataMember]
public uint RoomId { get; set; }
}
When I reference my service in client application,I only see Room
class,Can any body explain me why contract for Department and Section
class are not available at client side.