Hello.
The preposition in the sentence is under. A preposition is a word meaning where the noun is in the sentence, the noun is tree, the preposition is under.
I think that first you would have to know the topic you need to write about, then Create an outline for (What you will put in each paragraph), Have all of your facts looked up, prepared and on a scrap peice of paper. Write the essay on paper, proof read, fix errors, rewrite, and Type ( If you have to or want to).
I'm not actually sure, however, this is how I make essays and I hope this helps ^-^
Brutus and Cassius lose the fight they began in the plot to assassinate Caesar. In battle, these two conspirators are defeated by Octavius and Antony.