Peanuts are from a botanical perspective not classified as "nuts", "tree nuts". Instead, they belongs to the botanical family of legumes (peas, beans, lentils, soy, chick peas, lupine, etc.).
Most peanut allergic persons can eat legumes without any problems. A low number of peanut allergic persons (about 5%) have, however, an allergy to other legumes such as soy or beans.
Nevertheless, 25-50% of all peanut allergy sufferers develop allergic reactions to tree nuts (such as e.g. walnut, cashew, hazelnut, almond, pistachio, pecan, brazil nut or macadamia), despite the affiliation of tree nuts to a different botanical family.