The parts of the respiratory system that divide into smaller and smaller tubes in a pattern resembling the branches of a tree are the bronchi.
Once air enters the trachea, it splits into the left and right primary bronchi, which then divide into secondary (lobar) bronchi, and further into tertiary (segmental) bronchi, eventually leading to smaller bronchioles. This branching pattern is often compared to a tree structure, reflecting the progressive division of the air passages. The trachea, while it is the main airway, does not have the same extensive branching pattern as the bronchi.