How to detect Head Blocker

How to detect  head Blocker

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SET NOCOUNT ON
SET CONCAT_NULL_YIELDS_NULL OFF
GO
SELECT SPID, BLOCKED, REPLACE (REPLACE (T.TEXT, CHAR(10), ' '), CHAR (13), ' ' ) AS BATCH
INTO #T
FROM SYS.SYSPROCESSES R CROSS APPLY SYS.DM_EXEC_SQL_TEXT(R.SQL_HANDLE) T
GO
WITH BLOCKERS (SPID, BLOCKED, LEVEL, BATCH)
AS
(
SELECT SPID,
BLOCKED,
CAST (REPLICATE ('0', 4-LEN (CAST (SPID AS VARCHAR))) + CAST (SPID AS VARCHAR) AS VARCHAR (1000)) AS LEVEL,
BATCH FROM #T R
WHERE (BLOCKED = 0 OR BLOCKED = SPID)
AND EXISTS (SELECT * FROM #T R2 WHERE R2.BLOCKED = R.SPID AND R2.BLOCKED <> R2.SPID)
UNION ALL
SELECT R.SPID,
R.BLOCKED,
CAST (BLOCKERS.LEVEL + RIGHT (CAST ((1000 + R.SPID) AS VARCHAR (100)), 4) AS VARCHAR (1000)) AS LEVEL,
R.BATCH FROM #T AS R
INNER JOIN BLOCKERS ON R.BLOCKED = BLOCKERS.SPID WHERE R.BLOCKED > 0 AND R.BLOCKED <> R.SPID

)
SELECT N' ' + REPLICATE (N'| ', LEN (LEVEL)/4 - 2) + CASE WHEN (LEN (LEVEL)/4 - 1) = 0 THEN 'HEAD - ' ELSE '|------ ' END + CAST (SPID AS NVARCHAR (10)) + ' ' + BATCH AS BLOCKING_TREE FROM BLOCKERS ORDER BY LEVEL ASC
GO
DROP TABLE #T
GO