Hidden sources of Tree nuts

Almonds, walnuts, cashews and similar. (Stop immediately if you have a known allergy.)

Where it hides

Pesto and some Middle Eastern sauces — traditional pesto uses pine nuts or almonds as a base ingredient
Nut oils used as finishing oils (walnut, almond) — added at the end of cooking for flavor, easy to miss on a menu description
Almond or cashew flour in gluten-free baked goods — nut flours are a common wheat substitute in GF recipes
Cashew- or almond-based dairy alternatives (milk, cheese, yogurt) — marketed as "dairy-free" without emphasizing the nut base
Flavored liqueurs and coffee syrups (amaretto, Frangelico) — named for almond/hazelnut flavor and sometimes made with actual nut extract
Mortadella and some charcuterie — pistachios are a traditional studded-in ingredient in these cured meats, easy to miss when you're not expecting nuts in a deli item

Information only — not medical advice or a diagnosis. Settle structures a self-experiment and helps you track what you observe.