如何根据SQL Server中所有负责人的销售情况获得直属下属的总销售额？

Question

结构如下：

ID_EMPLOYEE   ID_EMPLOYEE_BOSS     LEVEL
        -------------------------------------------
            100           NULL                1
            201           100                 2
            202           100                 2
            301           201                 3
            302           201                 3
            303           202                 3
            304           202                 3
            401           302                 4
            402           302                 4
            403           302                 4
            N             N-1                 N

销售结构

ID_EMPLOYEE           SALE        DATE
    401               1100.00     2015-06-07
    402               1500.00     2015-06-05
    403               1400.00     2015-06-25
    303               5000.00     2015-05-25
    304               8250.00     2015-05-25

我试过这个

WITH Sales_CTE (ID_EMPLOYEE, SALE, MONTHS)
AS
(
    SELECT ID_EMPLOYEE, sum(SALE), DATEPART(mm,DATE)
    FROM SALES
    GROUP BY ID_EMPLOYEE, DATEPART(mm,DATE)
)
SELECT JE.ID_EMPLOYEE, OS.SALE, OS.MONTHS,
    JE.ID_EMPLOYEE_BOSS, OM.SALE, OM.MONTHS
FROM EMPLOYEES AS JE
    JOIN Sales_CTE AS OS
    ON JE.ID_EMPLOYEE= OS.ID_EMPLOYEE
    LEFT OUTER JOIN Sales_CTE AS OM
    ON JE.ID_EMPLOYEE_BOSS= OM.ID_EMPLOYEE
    WHERE ID_EMPLOYEE_BOSS= 302
ORDER BY JE.ID_EMPLOYEE_BOSS;

目前我只能立即看到销售员工级别n-1，但我想表现如下。例如，员工100可以看到

ID_EMPLOYEE  SALES    MONTH
201           4000    6
202          13250    5

这n级