A pearl onion is a type of tree onion grown mostly for pickling as a cocktail onion. However because of its unique diminutive appearance and much sweeter than bulb onion taste it has found use in dishes ranging from middle 20th century American casserole dishes such as succotash to sweetly flavored onion relishes in Indian cuisine. A pearl onion tree will take up to 2 years to make sufficiently sweet onions for sale.