Recursive Function

I am trying to write a recursive function which allows me to provide a hierarchical structure from an employee table but I am getting an error

Server: Msg 512, Level 16, State 1, Procedure GetEmployee, Line 10
Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.


Is there a way in which I can write a recursive function to do this. Or would I need to use cursors, multiple functions???
Any help or examples would be great. Thanks for your help

CREATE FUNCTION GetEmployee(@EmpID as int)
RETURNS @Employee Table
(
StaffNo int,
ParentStaffNo int
)
AS
BEGIN
DECLARE @ManagerID int
SET @ManagerID = (SELECT [id] FROM eii.dbo.test WHERE Parent_ID = @EmpID)

IF @ManagerID IS NOT NULL and @ManagerID > '' and @ManagerID <> @EmpID
INSERT INTO @Employee
SELECT [id],parent_id FROM eii.dbo.test Where [id] = @ManagerID
UNION
SELECT * FROM GetEmployee(@ManagerID)


RETURN
END