Dear Rabbi Weiman,
For you, what is the religious significance of a tree as a symbol?
Thanks for your question.
A tree as an analogy is used in many places as the symbol of mankind or an individual. Similar to the way a tree with a lot of roots is strong, so too a man with wisdom is strong. While branches may show off, the runs are the strength. While fruit, i.e. good deeds may be the most liked by others, they cannot happen without wisdom.
The tree is used as metaphor for a variety of things. It is a versatile thing, it gives shade, fruit, grows, dies, etc. So the possibilities for metaphor are many. In the Torah from the beginning with the Garden of Eden down into the Talmud the tree is an oft used symbol.
There is a popular kabbalist mussar work called The Palm Tree of Devora. The famous set of Sefirot in Kabbalah is usually referred to as the Tree of Life.
However, since actual trees have been used as idolatry, the visual picture of a tree is not often used in graphics or artistic designs on Judaica.