I see that you are using transactions.   Good.   Bulk inserts are often speeded up by disabling indexes on the table for the duration of the update.   When the indexes are re-enabled, they are calculated once for the whole data set.

I cannot easily see (because of the lack of <code> tags) whether you are preparing the query each time (you don’t need to), and whether you are using placeholders and bound parameters (you should be).