How to store multiple classes data into XML file using wcfservice?

This is my code

public void Add(Employee newEmployee)
        {
            XDocument doc = XDocument.Load(HttpContext.Current.Server.MapPath("StudentDB.xml"));
            //doc.Element("NewEmployees");
           empList.Add(new Employee
            {
                EmpNo = newEmployee.EmpNo,
                EmpName = newEmployee.EmpName,
                DeptName = newEmployee.DeptName,
                AllDepart = new List<Department> { new Department() { DeptNo = newEmployee.AllDepart[0].DeptNo, Dname = newEmployee.AllDepart[0].Dname, Location = newEmployee.AllDepart[0].Location } },

                AllSales = new List<Sales> { new Sales() { SName = newEmployee.AllSales[0].SName, Orders = new List<Order> { new Order() { Oid = Convert.ToInt32(newEmployee.AllSales[0]), OName = "ebay" } } } },
                Purchages =new List<Purchage> { new Purchage () { Id=Convert.ToInt32(newEmployee.Purchages[0]),IName=newEmployee.Purchages[0].ToString()}}
               
            });
             doc.Save(HttpContext.Current.Server.MapPath("StudentDB.xml"));
        }

where is mistake in my code above.