Pollen from various Fagales tree species prolongs the season and makes tree pollen allergy a major health problem. Despite involving the same causative allergens, allergy immunotherapy (AIT) treatment habits differ significantly across different geographical regions. Diagnosis and treatment with AIT in patients allergic to tree pollen were discussed by a group of German medical experts who give practical recommendations based on the available data. Regulatory perspective: According to current guidelines on allergen products, birch pollen are the representative allergen source of the birch homologous group including several Fagales trees based on sequence and structural similarity of their allergen proteins. Immunological perspective: A high level of IgE cross-reactivity towards allergens from the birch homologous group has been observed in basic research and clinical trials. Clinical perspective: Clinical trial data show that the efficacy of birch pollen AIT is not only related to birch pollen allergy but extends to pollen from other trees, especially alder, hazel and oak. In order to optimize diagnosis and treatment of tree pollen allergy, the experts recommend to focus diagnosis and respective treatment with AIT primarily to birch as the representative allergen of the Fagales tree homologous group, but further diagnostics may be needed for some patients to determine adequate treatment.