Acacia confusa

According to wikipedia: "Acacia confusa is a perennial tree native to South-East Asia.
Some common names for it are Acacia Petit Feuille, Taiwan acacia, Formosa Acacia, Small Philippine Acacia, Formosa Acacia (Taiwan Acacia) and Formosan Koa. It grows to a height of 15m. The tree has become very common in many tropical Pacific areas, including Hawaii, where the species is considered invasive"

Mature trees flowering in early Summer. Flowers individually very small, grouped many together in spherical yellow heads about 0.5 cm across. The tiny yellow flowers attract bees and other insect to collect some pollen. Fruit a flattened pod, to 4 - 9 x 1 cm, dark brown when dry, containing four to eight seeds.