The earliest Christmas decorations for trees made the use of fruits, sweets, and baked sweetmeats. Slowly, these were replaced by hand-blown Christmas glass ornaments. It became the symbol of the culture and Christmas celebrations.
In the late 1800s, entrepreneur F.W. Woolworth had the genius idea of using these as a part of commercial-grade Christmas decorations in the USA. It is how the glass ornaments came from Germany to the USA and later to all parts of the world. The round shape of the baubles originated from replacing the fruits, nuts, and baked goods and hence, attained this particular design.