Try ::
WITH CTE_Node(
NodeID,
NodeRigth,
NodeLeft,
Level,
RigthOrLeft
)
AS
(
SELECT
NodeID,
NodeRigth,
NodeLeft,
0 AS Level,
'P'
FROM Node
WHERE NodeID = 1
UNION ALL
SELECT
Node.NodeID,
Node.NodeRigth,
Node.NodeLeft,
Level + 1,
CASE WHEN CTE_Node.NodeLeft = Node.NodeID THEN 'R' ELSE 'L' END
FROM Node
INNER JOIN CTE_Node ON CTE_Node.NodeLeft = Node.NodeID
OR CTE_Node.NodeRigth = Node.NodeID
)
SELECT DISTINCT RigthOrLeft,
COUNT(NodeID) OVER(PARTITION BY RigthOrLeft)
FROM CTE_Node