The description of the tree in this verse is symbolic for Nebuchadnezzar who appears to be the ingenious king who takes the world to unprecedented heights through his architecture and buildings. Those who visited Babylon at that time saw a city that sparkled with culture and art—a beautiful, magnificent city. Nebuchadnezzar had ordered 53 large and magnificent temples to be built in the city, as well as 955 smaller shrines, and 384 altars. He also had magnificent palaces built in the city that included extensive libraries. He had an eighty metre wide moat built around the city. He also had a double wall constructed around Babylon. The wall was so wide that his army chariots could drive on top of it. He had caused hanging gardens to be installed that were considered one of the marvels of the ancient world.
The structures that he had erected were decorated with beautiful animal motifs, both on the inside and the outside of those buildings. With this knowledge, you will understand why we read that the tree in the dream also gave shade to the animals under it and that birds were found in the branches of this tree.
21 whose leaves were beautiful and its fruit abundant, and in which was food for all, under which beasts of the field found shade, and in whose branches the birds of the heavens lived