Trees are an important cause of pollen allergy as they are widespread & dense in the human environment and they produce huge quantities of pollen. You inhale this pollen in the air which can lead to allergic symptoms like sneezing, stuffy nose & watery eyes. This allergy maybe seasonal or it may persist for a long time. You should stay indoors in those seasons which worsen your condition or on dry windy days and also wear a mask when pollen counts are high.