I am familiar with a Passover seder, but what is a Tu BiShvat seder?
Tu BiShvat (Hebrew for the 15th day of the Hebrew month of Shvat) is the new year of the trees.
Why do we celebrate Tu BiShvat, the Jewish “New Year of the Trees,” in the middle of winter?
Tu BiShvat, called the "New Year of the Trees," falls at a seemingly incongruous time of year.
Maccabees
The family of five sons who led the revolt against the Hellenization of Jerusalem and became the heroes of the Hanukkah story.
Arbaah minim
Literally, “four species.” The Torah specifies four species to bring together on Sukkot. The four species are: lulav (branches of palm trees), etrog (citron), hadasim (myrtle branches), and aravot (willows) (Leviticus 23:40).
Why is caring for the environment emphasized on Tu BiShvat?
Tu BiShvat is a minor festival whose provenance dates only to the time of the Second Temple. However, the kabbalists who clustered around the great fifteenth-century mystic Isaac Luria of Safed placed great weight on the holiday, creating new festivities, gatherings at which hymns were sung, fruit (particularly carob) was eaten, and four cups of wine were taken (as in the Passover seder).