You should start from the very beginning. Reading One Piece manga in sequential order helps you understand the character growth and the evolving story arcs better. There are no major detours or alternate reading orders necessary.
The funniness of a tree comic often comes from creative imagination. Maybe the tree has a crazy personality or gets into wacky predicaments. Sometimes, it's the contrast between the serious image of a tree and the comical events surrounding it that makes it funny.
The common themes could include the struggle to find purpose in later life and the pain of being overlooked. Emotions might range from quiet desperation to brief moments of hope.
There's one called 'The Lumberjack Laughs' where the woodworker keeps making crazy mistakes that are hilarious. It's funny because of the unexpected situations and the character's reactions.