A Poison Tree is written in quatrains. This straightforward grouping of sets of four lines is one of the simplest and most recognisable poetic forms.
The poem has four stanzas. Each stanza consists of a pair of rhyming couplets in the regular repeated pattern aabb. The rhythm of the poem is also straightforward and regular which makes it very easy to read, though not necessarily to understand. The straightforward and seemingly simple way in which Blake has written this poem contrasts with the very complex human emotions he is describing.
The poem also contains two clear turning points which help the reader to understand the character of the speaker. The first comes after the opening two lines and shows the difference in how the speaker handles a difficult situation in two separate cases. In the second, symmetry is introduced in the final two lines and shows the speaker's reaction to what has happened. The wording at this point is ambiguous. It is a new day and a new beginning but the result of the speaker's untold anger is still there to see. This makes the reader continue to think about the poem after they have finished reading it.
The vocabulary is simple (even if some of the words are unfamiliar today). Notice the following:
All of the above makes the poem seem like a piece of verse for children and like a simple nursery rhyme with a clear moral message to be learned. The use of 'and' particularly resembles that of a child telling a story. A difficult message is wrapped up in a form and structure which is deliberately simple and using very straightforward vocabulary, to get its point across.