Look for fruit that are green, turning brown when mature in the fall. The leaves are “horseshoe” shaped, meaning that each fruit has two leaves that grow from opposite sides of the fruit. The flowers form double-leafed, wing-shaped fruits. The paired “wings” connect at the fruit and are oriented to each other at a 60 to 90 degree angle. The fruit should measure about 1 inch (2.54 cm) long, including both “wings.” The wings of a sugar maple grow parallel to one another. The fruit are technically referred to as “samara,” and may also be referred to as a “key.” These fruits are sometimes referred to as “seeds.” However, fruit is the correct designation, as the seeds are located inside the fleshy tissue of the sugar-maple fruit. Each sugar maple fruit, located between the two horseshoe-shaped leaves, will have a paired structure. Two distinct fruits, each the size of a small pea, will look as though they have been fused together in the center of each fruit.

TL;DR in Vietnamese:
Hái một quả nhỏ trên cây. Đo kích thước quả. Nhận diện cấu trúc hạt đôi.