Maintain the top parent record in a hierarchy. Here we specify the hierarchy level in the query as we traverse the hierarchy. Ultimately we can select only the records at the highest level giving us the top parent record at every step in the hierarchy.

topparenthierachy.sql

CREATE TABLE #Test (CompanyID INT, CompanyName VARCHAR(20), LinkedCompanyID INT)
INSERT INTO #Test
SELECT  1, 'Company A',   NULL UNION
SELECT  2, 'Company B',   1 UNION
SELECT  3, 'Company C',   2 UNION
SELECT  4, 'Company D',   2 UNION
SELECT  5, 'Company E',   4 UNION
SELECT  6, 'Company F',   3 UNION
SELECT  7, 'Company G',   NULL

;WITH CTE AS
(   SELECT  *, 0 [Level]
    FROM    #Test
    UNION ALL
    SELECT  CTE.CompanyID, CTE.CompanyName, #Test.LinkedCompanyID, Level + 1
    FROM    CTE
            INNER JOIN #Test
                ON CTE.LinkedCompanyID = #Test.CompanyID
    WHERE   #Test.LinkedCompanyID IS NOT NULL
)

SELECT  c.CompanyID, c.CompanyName, c.LinkedCompanyID
FROM    (   SELECT  *, MAX([Level]) OVER (PARTITION BY CompanyName) [MaxLevel]
            FROM    CTE
        ) c
WHERE   MaxLevel = Level

DROP TABLE #Test