An expository essay is written to explain or recount a certain topic. So if the topics are similar then you can compare and contrast and explain the differences and similarities. Important structure/points to cover would be to make sure that you are emphasizing you main point. I like to use that are able to take a direct object because they make the essay flow very nicely, and to restate your hypothesis in your conclusion with emphasis on how your facts have supported it.
Hope this helps! If you any any other questions or would like further explanation just let me know! :)
