This tree is a weedy pest from Central and South America. Botanists have a hard time figuring if its in the family Urticaceae, Moraceae or Cecropiaceae. The species is part of a complex (according to this site), so there are two other species that are very closely related, making the distinction between them slightly perplexing.
In its native habitat, Azteca (biting) ants inhabit the hollows of the tree and are thought to protect it from herbivores. Over here in Singapore though, the tree seems to do quite well without need of the ants. The flowers are borne on the finger-like spikes at the end of the long stalk near the crown of the tree.
Not to be a sensationalist but this plant is listed as ” 100 of the World’s Worst Invasive Alien Species” by the Invasive Species Specialist Group (ISSG) which is part of the World Conservation Union (IUCN).
Photo taken at the Singapore Zoo.