Tree nut allergy is really a category of allergies. Just because someone is allergic to one type of tree nut, doesn't necessarily mean they are allergic to all of them. But there is an increased chance that they are allergic to more than one. Examples of tree nuts include walnuts, almonds, hazelnuts, cashews, pistachios, and Brazil nuts. Children with tree nut allergies are not likely to outgrow them and are generally advised to also stay away from peanuts to avoid cross-contamination.