Many Broadleaf trees have white flowers. Use this option to identify these trees. Usually the flowers are only present for a few weeks and some flower in spring before the leaves. Look at the size and shape of the flower and also whether it is single or in long spikes or tails or compact clusters. Some Flowering Cherries have white or pink flowers.
One flower from one bud
Cherry Plum (March)
Many flowers from one bud
Wild Cherry, Pear, Crab Apple, Lime
Many flowers in a flat cluster
Elder, Rowan, Whitebeam, Hawthorn
Many flowers in a narrow cluster which may be upright (Horse Chestnut and Cherry Laurel) or hang down in a tail (False Acacia, Bird Cherry, Manchurian Cherry).