Updating a chain of records by a CTE - SQL Server 2005

Hi,

I've the following SQL Server 2005 table:

CREATE TABLE [dbo].[WOr](
	[WO] [varchar](10) NULL,
	[WO_Parent] [varchar](10) NULL,
	[WO_Group] [varchar](10) NULL
) ON [PRIMARY]

with these test values:

INSERT INTO [WOr] ([WO] ,[WO_Parent] ,[WO_Group])
VALUES ('2000', NULL, NULL)
INSERT INTO [WOr] ([WO] ,[WO_Parent] ,[WO_Group])
VALUES ('2001', '2000', NULL)
INSERT INTO [WOr] ([WO] ,[WO_Parent] ,[WO_Group])
VALUES ('2002', '2001', NULL)
INSERT INTO [WOr] ([WO] ,[WO_Parent] ,[WO_Group])
VALUES ('2003', '2002', NULL)
INSERT INTO [WOr] ([WO] ,[WO_Parent] ,[WO_Group])
VALUES ('5000', NULL, NULL)
INSERT INTO [WOr] ([WO] ,[WO_Parent] ,[WO_Group])
VALUES ('5001', '5000', NULL)
INSERT INTO [WOr] ([WO] ,[WO_Parent] ,[WO_Group])
VALUES ('5002', '5001', NULL)
INSERT INTO [WOr] ([WO] ,[WO_Parent] ,[WO_Group])
VALUES ('5003', '5002', NULL)

I need to updating the WO_group column with the WO value of the first item of the chain of records.

In this sample, a chain begins with the record having WO = 2000. This recors hasn't any parent record. The record having WO = 2001 has the record with WO = 2000 as a parent and so on.

The goal is to update the chain from WO = 2000 to WO = 2003 setting the WO_group = 2000.

I'm trying to use a CTE:

WITH CTE(WO, WO_parent, wo_group, Level) AS
(
SELECT WO, WO_parent, wo_group, 0 as Level
FROM WOr WHERE WO_Parent IS NULL
UNION ALL
SELECT W1.WO, W1.WO_parent, w1.wo_group, Level + 1
FROM WOr as W1 INNER JOIN CTE as W2
on W1.WO_parent = W2.WO
)

but I can setting the WO_group column only for the records without a parent.

Any suggests to me, please? Thanks