By default you cannot add more items of certain product to a bundle, but there is a workaround for this scenario.
You could create a new product which would by itself represent 10 units of Product A in its standard way. You would multiply the price by 10 so that the price is a correct and then used this product in your bundle. This seems to be the easiest way of doing something like this.
You can also vote for this idea on the UserVoice portal.