View the video and take notes about the artist, his history, and artistic goals.
Look at each of the links of Corot paintings, read the captions, and notice the specificity and, at the same time, the painterly qualities of the trees.
Corot – Oaks at Bas-Breau, Fontainbleu
Corot – The Ferryman
Look at the images of trees on the first 3 pages of the search and copy 3 that you especially like in your sketchbook.