Tree
In general, trees represent the deepest and most significant intellectual concepts: the ones that come to us most directly from the Lord. This varies depending on us and our states: the people of the Most Ancient Church, who were in a state of loving the Lord, understood truth automatically and internally through what the Writings call "perception"; people in lower states (including most of us) have to work a little harder to learn it from the Word and by willing to follow the Lord. In other parts of the Bible, especially in the prophets and New Testament parables, the meaning of "tree" is broader, meaning not just a person's intellectual concepts but the whole person.
'Trees,' as in Joel 1:10-12, signify knowledges.
Psalms 72:13-15
13
He will have pity on the poor and needy. He will save the souls of the needy.
14
He will redeem their soul from oppression and violence. Their blood will be precious in his sight.
15
They shall live, and to him shall be given of the gold of Sheba. Men shall pray for him continually. They shall bless him all day long.