A flower cluster with flower stalks that are proportionally longer than the upper stalks, resulting in a flat or slightly convex head of flowers is known as Corymb.
Corymb is a botanical word describing an inflorescence in which the outermost blooms are carried on longer pedicels than the innermost, bringing all flowers up to the same level.
Flowers in a corymb structure can be in a convex or flat form and can be parallel or alternate.
Umbel:
A flower cluster is characterized by almost equal-length stalks that emerge from a shared center to form a flat or curved surface, as seen in the parsley family.
An umbel is a type of inflorescence that consists of several short flower stalks (called pedicels) that extend out from a central point, like umbrella ribs.
The word umbella comes from the Latin word umbrella, which means "parasol, sunshade." It was first used in botanical terminology in the 1590s.