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.
Heaven and Hell #20
20. HEAVEN IS DISTINGUISHED INTO TWO KINGDOMS
As there are infinite varieties in heaven, and no one society nor even any one angel is exactly like any other, 1 there are in heaven general, specific and particular divisions. The general division is into two kingdoms, the specific into three heavens and the particular into innumerable societies. The details will be treated of in what now follows. They are termed kingdoms because heaven is called the kingdom of God.
Footnotes:
1. [Swedenborg's footnote] There is infinite variety and nowhere anything the same as another (Arcana Coelestia 7236, 9002). Also, in the heavens there is infinite variety (Arcana Coelestia 684, 690, 3744, 5598, 7236); and those varieties are varieties of good (Arcana Coelestia 3744, 4005, 7236, 7833, 7836, 9002); and thus all the societies in the heavens and every angel in a society are distinguished from each other (Arcana Coelestia 690, 3245, 3519, 3804, 3986, 4067, 4149, 4263, 7236, 7833, 7836); but still all make one by love from the Lord (Arcana Coelestia 457, 3986).