Query to calculate SUM of below top level Childs calculated amount

I have a Table TestPoolCalc, I need to show current node amount + sum of below top level Childs calculated amount. Please see the expected output

Table Script and Data

 CREATE TABLE [dbo].[_TestPoolCalc](
    [PoolID] [varchar](50) NULL,
    [ParentPoolID] [varchar](50) NULL,
    [Amount] [numeric](18, 2) NULL
) ON [PRIMARY]
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 1
', N'ROOT', NULL)
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 1.1
', N'Pool 1
', NULL)
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 1.1.1
', N'Pool 1.1
', NULL)
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 1.1.1.1
', N'Pool 1.1.1
', CAST(-12500.00 AS Numeric(18, 2)))
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 1.1.1.2
', N'Pool 1.1.1
', CAST(-12500.00 AS Numeric(18, 2)))
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 1.1.2
', N'Pool 1.1
', CAST(-25000.00 AS Numeric(18, 2)))
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 1.2
', N'Pool 1
', CAST(25000.00 AS Numeric(18, 2)))
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 1.3', N'Pool 1
', CAST(-50000.00 AS Numeric(18, 2)))
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 2', N'ROOT', NULL)
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 2.1', N'Pool 2', NULL)
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 2.2', N'Pool 2', NULL)
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'Pool 2.3', N'Pool 2', CAST(75000.00 AS Numeric(18, 2)))
GO
INSERT [dbo].[_TestPoolCalc] ([PoolID], [ParentPoolID], [Amount]) VALUES (N'ROOT', NULL, NULL)
GO

Way I tried

  WITH p AS (SELECT            
   a.ParentPoolID, a.PoolID 
   , CAST(a.PoolID AS VARCHAR(MAX)) AS path    
   , len(CAST(a.PoolID AS VARCHAR(MAX))) lpath    
   , a.Amount    
   
  FROM _TestPoolCalc a    
  WHERE a.ParentPoolID = 'Root'    
        UNION ALL    
  SELECT    
   pp.ParentPoolID, pp.PoolID   
   , p_2.path + '>' + pp.PoolID AS path    
   , len(p_2.path + '>' + pp.PoolID) lpath    
   , pp.Amount   
    
  FROM _TestPoolCalc pp     
     
  JOIN p AS p_2 ON pp.ParentPoolID = p_2.PoolID 
  )    
SELECT PoolID,ParentPoolID, path    
,Amount
,isnull((select sum(isnull(p1.Amount,0.0)) from p p1 where left(p1.path,p.lpath) = p.path and p.poolid <> p1.PoolId ),0) CalculatedAmount     
FROM  p
order by path

Expected output

Using your test data:

WITH p AS (
    SELECT  poolid AS main, t.Amount, t.PoolID AS parent
    FROM    _TestPoolCalc t
    UNION ALL
    SELECT  p.main, tc.amount, tc.poolid
    FROM    p
    INNER JOIN _TestPoolCalc tc
        ON  tc.ParentPoolID = p.parent
  )    
SELECT  Main, ISNULL(SUM(Amount),0) AS total
FROM    p
GROUP BY Main

For each node, i gather it and all the children under it. By keeping the PoolID as main, it becomes very easy to gather the final result, although, this code does traverse levels multiple times which can have some performance implications.

Output:

You can always remove the ROOT if you're not interested in it.