What is the theme of the poem a poison tree use evidence from the text to support your answer

Although William Blake's "A Poison Tree" is about anger, the central theme and message is about the suppression of anger. The poem argues that like a tree, anger grows if one suppresses it.The speaker of the poem reveals to his friend that he is angry, and the anger dissipates. But when the speaker hides his anger from his enemy, the anger grows, much like a tree. The fact that the tree is "poison" tells us that, by ignoring or suppressing anger, we are also poisoned. The apple that appears on the tree of anger symbolizes that poisonous effect. The final line is ominous; the speaker's delight at the "foe outstretched beneath the tree" offers a warning about what happens when we suppress our anger. If we ignore or deny our feelings, we will become wicked, bitter, and even vengeful.

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