Becoming ISA certified

I’m coming up on my one year mark doing tree work, I’ve found a good passion in this industry and I’m thinking of progressing myself in it. The 2 ways I know of to become certified is to work under an arborist (I believe it’s 3 years but could be wrong) and schooling. I don’t work for a company with arborists but I like who I work with. What degree or extent of schooling do I need to one day test to become certified? Is it possible for me to do this online at my own pace so I can work, study and not totally burn myself out?