The Jewish mystics of the 17th century, the Kabbalists, created a special ritual—modeled after the Passover seder—to celebrate God's presence in nature.
The Tu BiSh'vat seder, full of imagery and symbolism, is divided into four sections that represent the four seasons. This seder also is divided into four mystical “spheres,” each of which represents a different relationship between humans and the earth: Assiya (Actualization), Yetzira (Formation), Beriah (Creation), and Atzilut (Nobility).
As with the Passover seder, the Tu BiSh'vat seder evolved to include four cups of wine or grape juice, but in varying shades of red, which represent the seasons: white for the bleak time of winter, white with a bit of red to represent the earth’s awakening in early spring, red with a bit of white representing the blossoming of late spring, and dark red to represent the fullness of all the growing plants and vegetation along with the heat of summer.
Finally, various fruits are consumed in each part of the seder: those with a hard shell, those with a pit that cannot be eaten, and those that are completely edible.