On Shavuot the priests bring the “two loaves,” an offering made from leavened bread, unlike most meal offerings, which may not be brought from leavened bread. The Sages explain why Shavuot is the time for this offering.

For what reason did the Torah say: Bring the two-loaves offering on Shavuot? Because Shavuot is the beginning of the time of the ripening of fruits that grow on a tree. The Holy One, blessed be He, said: Bring the two loaves before Me on Shavuot so that the fruits of the tree will be blessed for you. (Rosh HaShana 16a)