Trees are not simple in the Torah. We are forbidden from using trees to make idols. We are told to never worship trees, and indeed, nothing in the Tabernacle/Mishkan had visible wood at all. That all seems to suggest a negative symbolism for trees in general.
On the other hand, the first named trees are the Tree of Life, and the Tree of Knowledge of Good and Evil. These trees were mystical source of knowledge and even immortality! Separately, we are forbidden to cut down fruit trees. Which all sounds pretty pro-tree. So which is it?
And why does the Torah tell us that someone hung on a tree, specifically, must be buried?
I think the answer is found by looking at trees in the text a little more carefully. Here is the first mention:
And God said, “Let the earth sprout vegetation: seed-bearing plants, fruit trees of every kind on earth that bear fruit with the seed in it.” And it was so.
Trees are the first plants in the Torah that, we are told, contain their own seeds. Which tells us that trees are somehow special, because they are in it for the long haul. Trees are very long-lived (almost every kind of tree lives longer than a person does, and some can live for thousands of years!) But they also, thanks to the seeds they carry within their fruit, are inherently invested in future generations.
Indeed, I think we could logically argue that in a symbolic sense, trees are an early prototype for mankind ourselves! Consider:
1: Trees are anchored in the earth and reach for the sky – just as the Torah commands people to connect with the earth and then, using all our faculties, seek to form a relationship with heaven.
2: Trees feed others, supporting life within and without its perimeter – just as people are encouraged to support and promote life wherever we can.
3: Trees, thanks to their long life and seeded fruit, invest in the future, putting their own energies into the next generations – just as people are commanded to have children and teach them to be good and holy people.
4: Trees even change their environment. In the soil, in the wind and the rain and the sunlight, trees have an impact on nature and on other living things – just as people are meant to do.
Mankind has many capabilities beyond those of trees, of course. But the symbolic links are extremely strong and consistent with the Torah goals for mankind.
Which might help explain a verse that produces a myriad of questions:
If any party has sinned and is adjudged for death and is put to death, and you string up the body on a tree, you must not let the corpse remain on the tree, but must bury it the same day.
Why is the tree in this verse? After all, if you are supposed to bury a body anyway, surely it does not matter that it was hung on a tree, right?!
But the verse is specific, which raises the firm question: what is the problem with a dead body on a tree?
I think the answer connects to a number of other commandments in the Torah that forbid short-circuiting the natural world – just as cooking a kid in its mother’s milk provides a dead-ended loop and is thus forbidden. The laws of incest, as well as many others, could also be understood in this light.
If trees are prototypes for humans, then stringing a dead body up on a tree is also a short-circuit. Dead people go against the purpose and importance of trees. A tree and a dead person are not meant to be together, and so if it should happen that they are put together (even according to legal principles), such a thing must not be allowed to remain. Trees represent life in its finest forms, indeed, it, like man, symbolically seeks to reconnect heaven and earth! So hanging a body on a tree perverts both the dead man and the living tree, in a way that is similar to boiling a kid in its mother’s milk.
Consider, too, that fruit (and seeds) hang from trees already. And that fruit and seeds are committed to, and invested in, future life. Hanging a dead person is incompatible with that mission.
[Note that this is part of a series explicating a single verse: Deuteronomy 21:23. All work was done in collaboration with @susanquinn, @kidcoder, @blessedblackmith and @eliyahumasinter. The full series can be found on creativejudaism.org]