BG Chap 15 - The secondary roots of the tree
The secondary roots are the impressions caused by attachment and repulsion born from enjoyment of various sense objects. They spread out everywhere in the world of men, and are causes of continued action. The impressions are said to be the roots because they are the causes of man’s tendency to act according to dharma or adharma. The main root (cause of the universe) is Brahmā, and the secondary roots (which cause actions and particular bodies) are the various impressions. These are compared to the tangled roots emanating from the banyan tree. They give rise to bondage of karma.