Inflorescence of onion is called

The inflorescence of onion is called Umbel.
An umbel is an inflorescence that consists of several short flower stalks (called pedicels) that spread from a common point, somewhat like umbrella ribs. The word was coined in botanical usage in the 1590s, from Latin umbella "parasol, sunshade".
The inflorescence in onion is umbel, in which the outside flowers bloom first and flowering progress to the inside. Some species produce bulbils within the umbels, and in some species, such as Allium paradoxum, the bulbils replace some or all the flowers.