In the first stanza of "A Poison Tree," the speaker says, "I told my wrath, my wrath did end" (2) and "I told it not, my wrath did grow" (4). The poem suggests that talking about emotions is an important part of dealing with them. It also suggests that not talking about our emotions, instead harboring and cultivating them, will lead to poisonous "fruit"—the poem's metaphor for the dire consequences of anger that's not dealt with properly. Trust us—that is one bad apple. The good news is, though, that we can avoid the speaker's grim fate. We've just got to get the bad stuff off our chest on a regular basis.
That's it. Let it all out. "A Poison Tree" suggests that anger—and perhaps other negative emotions—can be eliminated or contained by talking about them.
"A Poison Tree" shows us how anger begets more anger, attracting others' hate to our own. It's like a bad vibes magnet.