A wide range of aerosols, including dust, soot, and biological particles, can serve as ice nuclei, initiating the freezing of supercooled cloud droplets. This process significantly impacts cloud characteristics and, consequently, weather and climate. Some biological ice nuclei exhibit exceptionally high nucleation temperatures. Although Ice Nucleating Macromolecules (INMs) found in pollen are not the most active ice nuclei, they are abundant. This is evident from the widespread distribution of certain tree species, such as Betula pendula, and their presence throughout the trees' tissues (Felgitsch et al, 2018; Seifried et al, 2020). Recent studies have shown that certain tree-based INMs demonstrate ice nucleation activity above -10°C (Gute & Abbat, 2020; Murray et al, 2020). These findings suggest that INMs emitted from the biosphere may play a more significant role in atmospheric processes than previously understood. Our results show that Betula pendula INMs comprise three distinct classes active at -6°C, -15°C, and -18°C, each in different concentrations. We observed that freeze-drying and freeze-thaw cycles markedly alter their ice nucleation capacity. Heat treatments and chemical analyses suggest that these INM classes may be variable sized aggregates, with larger aggregates being more efficient at nucleating ice. This hypothesis aligns with previous studies on fungal and bacterial ice nucleators. Our research highlights the significance of birch INMs in atmospheric ice nucleation, not only because of their prevalence, but also due to their occasional but notable high nucleation temperatures.