Return List <T> with WCF Service

I got a class Employee, and each employee has a list of applied sheets. Is it possible to have a list AppliedLeavelike [DataMember]in WCF?

[DataContract]
public class Employee
{
    [DataMember]
    public string UserID { get; set; }

    [DataMember]
    public int EmployeeNumber { get; set; }

    [ForeignKey("EmployeeUserID")]
    [DataMember]
    public List<Leave> AppliedLeave
    {
        get { return _appliedLeaves; }
        set { _appliedLeaves = value; }
    }

    private List<Leave> _appliedLeaves = new List<Leave>();
    ...
 }

Is there any other way to do this?

thank you for considering this issue

I am expanding my question

This is my vacation class:

[DataContract]
public class Leave
{

    [Key()]
    [DataMember]
    public Guid LeaveId { get; set; }

    [DataMember]
    public string LeaveType { get; set; }

    [DataMember]
    public DateTime StartDate { get; set; }

    [DataMember]
    public string EmployeeUserID { get; set; }

}

it shows ServiceContract ---->

[ServiceContract]
public interface IEmployeeService
{
    [OperationContract]
    Employee GetEmployeeByUserId(string userId);

    [OperationContract]
    void AssignSupervisor(string userId, string supervisorUserId);

    [OperationContract]
    void DeleteEmployeeByUserId(string userId);

....
}

In the client application

EmployeeServiceClient employeeService = new EmployeeServiceClient ();

Employee Employee = employeeService.GetEmployeeByUserId (id);

But when the Employee collected from the service his Null displays for leaves,

Can someone help me? what did i do wrong here?