Treat ornamental hemlock with which oil product?

I have a small ornamental hemlock with a few branches covered in wooly adelgid. Tree looks to be some sort of weeping/dwarf cultivar- it’s weird but looks great where it is. Which product is best to use for treating the adelgid? I have read that horticultural Oil works. But also Neem Oil. And I don’t quite understand the distinction. Located in the northeast. I’d like to use whatever is least toxic to the tree and the rest of my yard. It is located near a well. Im patient, don’t mind doing repeated treatments over several years.