The Mishnah teaches that there the world is judged four time: on Pesach, Shavuos, Rosh Hashanah, and Sukkos. On the Yom Tov of Shavuos we are judged for the fruits of the trees. The Gemara explains that the Torah commands us to bring the shtei halechem on Shavuos since it is the season of the fruits of the trees, in order to bless the fruits of the trees.
The shtei halechem was a korban of wheat, if so how does it correspond to blessing the fruits of trees? Rashi answers: the shtei halechem was the first to be brought as a korban in the new year as it states בכורי קציר חטים. Afterwards we are permitted to bring all the first-fruits of bikurim. Rashi brings another answer of why wheat is brought as a korban for the fruits to be blessed. Rebi Yehudah says Adam sinned by eating from a wheat tree. Originally Adam was huge, however once he sinned Hashem shortened him. The passuk states by the curse to the snake, “on your stomach you shall crawl,” it too was shortened, and cut down. So too is with the wheat tree; it was shortened and cut down in size to be stalks. The Gemara brings that L’asid lavo the wheat will straighten up tall like a palm tree, from the valley to the tops of the mountains, and it will produce fresh bread! Therefore the wheat, from what is meant to be a wheat tree, is brought to bless the fruits of the trees.
The Magen Avraham brings that there is a custom to stand up trees in Shul and in houses for Shavuos as a remembrance that on Shavuos we are judged on fruits of the trees, and we should daven for them. The Gra however stopped this custom because the non-Jews would do this on their holiday.
The passuk states האדם עץ השדה, a person is a tree of the field. What is the similarity between a person and a tree? The Maharal explains that the trunk of a tree stands upright, so too a person stands upright, unlike animals which are leveled. A tree has branches on its sides, so too a person has hands on his sides. Also both trees and people have roots; a tree is nourished and draws its nutrients from roots in the ground, whereas a person draws his strength and assistance from his mazal-angel in heaven. A tree is a physical being, therefore its roots are in the ground, and its direction is to the ground which is the place of its sustenance. However a person is meant to be a spiritual being, therefore his head is on top of him, above the rest of his body, directed towards the heaven. Lastly, a tree provides sustenance to others, so too people who learn Torah strengthen Yiddishkeit and spirituality in others.
On Shavuos we daven for trees which are physical, and we daven for our growth in Torah. Just as a tree flowers, blossoms and bears fruit, so too a person who learns Torah and understands something new grows and flourishes.
May Hashem bentch the fruits of the trees; both the physical trees with its fruits, and ourselves, with our spiritual growth!