sum by individual group (tree)

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C#

SQL

LINQ

I have 3 tables; item_master, order & helper. my item structure is like:
General (level1)
|____Content (level2)
| |___GnMain (level3)
| | |__vb6
| | |__vb.net
| | |__c#
| | |__f#
| |______jq
| |______js
|____________java

my question is how can i get the individual sum of each level and insert it into the helper table if customer order for maybe 6 of the product. at different quantities each in one order.

one way is to update the helper table while inserting each item but this will cause performers problem if the levels increase and also if more items are in the customer's order.
that is

foreach item
call udf to get parent, grandparent, greatgrandparent etc as the case may apply
then
foreach parents update oldsum+newsum

please i need a way out or point me to an article that can solve this business need perfectly.

thanks every one in advance.