Building hierarchical order rows from hierarchical table structure

Question

I am looking for a tricky way to build hierarchical order rows from the following data:

SET NOCOUNT ON
GO

    DECLARE @DataSource TABLE
    ( 
        [Col001] CHAR(2)
       ,[Col002] CHAR(2)
       ,[Col003] CHAR(2)
       ,[Col004] CHAR(2)
    )

    INSERT INTO @DataSource ([Col001], [Col002], [Col003], [Col004])
    VALUES ('A1','B1','C1','D1')
          ,('A1','B1','C1','D2')
          ,('A1','B1','C2','D3')
          ,('A1','B1','C2','D4')
          ,('A1','B2','C1','D5')
          ,('A1','B2','C1','D6')
          ,('A1','B2','C1','D7')

    SELECT [Col001]
          ,[Col002]
          ,[Col003]
          ,[Col004]
    FROM @DataSource

SET NOCOUNT OFF
GO

And the result I am looking is something like this:

I know the source data and the results may look strange, but how I am getting them. In my real situation, I may get multiple columns, but each suggestion or idea will be appreciated.

Note: The [Level] order needs to be the same in the screenshot that I have provided. That's the real difficulty.

The idea is to preserve the connections:

Answer 1

If the order is important then try this:

select [Level],Val from
(
SELECT '0' as [Level], [Col001] as Ord, [Col001] as Val  FROM @DataSource
union 
SELECT '1' as [Level], [Col001]+[Col002] as Ord, [Col002] as Val  FROM @DataSource
union 
SELECT '2' as [Level], [Col001]+[Col002]+[Col003] as Ord, [Col003] as Val  FROM @DataSource
union 
SELECT '3' as [Level], [Col001]+[Col002]+[Col003]+[Col004] as Ord, [Col004] as Val  FROM @DataSource
) as T1
ORDER BY Ord,[Level]

Answer 2

I am not certain how you wish to determine the level Maybe something like this

    /*Union a select for each column and select distinct.
    I am assuming that column number - 1 is the level*/
    SELECT DISTINCT T1.Level,T1.Data
    FROM (
    SELECT 0 [Level],[Col001] [Data] FROM @DataSource
    UNION ALL SELECT 1, [Col002] FROM @DataSource
    UNION ALL SELECT 2, [Col003] FROM @DataSource
    UNION ALL SELECT 3, [Col004] FROM @DataSource
    ) T1