Hello,
What you're specifying should indeed push the tree globally. Potentially another option would be to set the workbook after construction using my_csv_tree.workbook = None, but that shouldn't be nessisary.
I don't suppose the version of SPy that you're using is before 184.3? There were some important bug fixes for globally pushing trees in that release. (Your version can be found using spy.__version__ or pip show seeq.)