Tree pollen allergies, particularly those caused by members of the Betulaceae family such as birch, alder, and hazel, are widespread and represent a significant burden on the healthcare system, with prevalence rates of 15–30%. Clinical presentation consists predominantly of allergic rhinitis or rhinoconjunctivitis, which can progress to allergic asthma. Allergen immunotherapy (AIT), through the induction of immunological tolerance to the triggering allergen, represents the only currently available disease-modifying treatment option for tree pollen allergy. In addition to subcutaneous immunotherapy (SCIT), sublingual immunotherapy (SLIT) in particular has established itself as an effective and safe therapy. Current randomized trials and real-world data demonstrate a significant reduction in symptoms in both adults and children, as well as evidence for the prevention of asthma development. Molecular insights into tree pollen allergens and advances in component-based diagnostics are enabling more precise patient selection and treatment optimization. Of particular importance here is the differentiation between an allergy to the major allergen of birch and homologous allergens of other tree species that show little or no cross-reactivity. The current findings on the diagnosis and treatment of tree pollen allergy are reviewed in this article.