The katakana characters below say risu (squirrel) for those who want to practice their calligraphy.
These relatively simple sketches are for practice. The first one is a squirrel.
The next sketch is a chipmunk.
A problem with a painting of a chipmunk and an oak tree is that the two are so vastly different in size. In order to make a composition work, they have to be closer in scale. That is why I only have a small portion of an oak tree in my painting. Another possibility may be to have a landscape with the chipmunk and oak branch (and leaf) in the foreground with a whole oak tree in the distant background.