Théodore Rousseau

Rousseau, Corot's friend and the central figure of the Barbizon school, drew trees as individuals. His pencil and pen studies of the oaks of Fontainebleau trace the whole branch structure from root to twig with a patience no one else had, and his etchings and cliches-verre carry the same structural truth into print. He was refused by the Salon for a decade and painted anyway.

Where Corot gives you the tree as a mass, Rousseau gives you the tree as an engineering drawing. A beginner needs both. Draw a Rousseau oak once, following the branch logic through every fork, and the Corot masses will sit on a skeleton you understand.