DECLARE @Item hierarchyid
SELECT @Item = [DirNode]
FROM [dev].[dbo].[Files]
WHERE ClientID = 2
    AND ProjectIDFilter=1055
    AND [DirNode] ='/3/3/'

SELECT [DirNode].ToString()
      ,[DirLevel]
      ,[ParentDirNode].ToString()
      ,[ClientID]
      ,[ProjectID]
      ,[ProjectIDFilter]
      ,[Name]
FROM [dev].[dbo].[Files]
WHERE ClientID = 2
    AND ProjectIDFilter=1055
    AND [DirNode].GetAncestor(1) = @Item