a tree: a large woody plant with a trunk, branches, and often fruit
This is the ordinary Greek word for a tree, a living plant large enough to bear fruit, cast shade, or shelter birds. It always points to a real tree, never to cut wood or timber (that is a different Greek word).
Much of its use in the Gospels comes inside a word picture. Jesus repeatedly holds up a tree and its fruit as an image of a person and that person's life: a good tree produces good fruit and a bad tree bad fruit, so a tree is known by what it yields. John the Baptist warns that the axe is already laid to the root of the trees, meaning that people who bear no good fruit face judgment. In each case the word itself still means a literal tree; the comparison to a person is carried by the sentence around it, not by any second meaning of the word.
Elsewhere it simply names trees in the world: the tiny mustard seed grows into a tree where birds nest, crowds cut branches from trees to spread on the road, and in Revelation the trees of the earth are scorched or protected as God's judgments fall. Across every setting the meaning holds steady.