With tree pollen counts already hitting peak levels in some parts of the United States, now is the time to start preparing for — and treating — your spring allergy symptoms. But before you head to a pharmacy, consider some measures you can take at home. And if you do need to resort to medication, here’s what to know about the various pills, sprays and shots available. Sign up for The Morning newsletter from the New York Times Your First Line Defense Doctors recommend first trying to limit your e