Hi Jean,
I think what you are asking for is INPUT ARRAY in a tree container. There are two enhancements requests in the system around this ...
Bz17159 - Support data input in Tree Views with INPUT ARRAY
Bz21799 - Support DISPLAY ARRAY CRUD triggers with Tree View
... contact your local support and get them to add your name to the list of requestors. It is a good time to ask for these now as the developers are starting to think about the 2.50 release and what to put in it.
I suspect for 17159 there would have to be an implicit INSERT ROW=FALSE, APPEND ROW=FALSE, DELETE ROW=FALSE so that rows weren't added or removed.
In the interim, have a look at the Bill of Materials demo in $FGLDIR/demo/Tree/bill-of-material. That uses buttons outside the array to change values inside the tree container.
Hope that helps
Reuben