The roots of a tree are said to show our connection with ourselves and the earth.
It could be more accurate to suggest that they signify our ability to belong to the practical side of life, to enjoy being here.
Spreading roots would indicate an ability to relate well to the physical, and, conversely, deep-rootedness would suggest a more self-contained attitude.
The trunk of the tree gives an indication of how we use the energies available to us, and also what exterior we present to the world.
A rough trunk suggests obviously a rough and ready personality, whereas a smoother trunk would indicate more sophistication.