Noun
tree onion (plural tree onions)
Allium × proliferum, a kind of hybrid onion with a cluster of bulblets where a normal onion would have flowers.
A. ×proliferum, tree onion The tree onion or Egyptian onion produces bulblets in the umbel instead of flowers, and is now known to be a hybrid of A. cepa × A. fistulosum. Source: Internet
This genus also contains several other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion ( Allium fistulosum ), the tree onion (A. Source: Internet