Ash.

This is an Ash tree coming into flower.
Ash before Oak you are in for a soak.
Oak before Ash you are in for a splash.

So we are in for a soak as the Oak is still in bud.

The Common Ash Fraxinus excelsior produces flowers in March before the leaves. Ash trees have a complex reproductive system. The flowers have no petals and may be male, female or bisexual. In any population some trees have only male flowers and produce pollen, some only female flowers and produce seeds and some have bisexual flowers and produce pollen and seeds.