In this poem Sylvia Plath assumes a persona, that of a personified tree. It is appropriate, given that her name, Sylvia, means related to woods and trees. She uses the device as an extended metaphor, describing the roots reaching into dark underground depths rather than the usual exposed trunk and branches.

This signifies the person, herself, who seems ordinary from the outside but has complex deep, dark depths within. Sylvia Plath struggled with depression and mental illness throughout her life.

Sylvia Plath uses three pronouns—“she,” “I,” and “you”—which can be read as the divided selves of one identity as well as three separate roles.

“She” not only signifies the elm tree but also the artistic detachment of the poet from both “I” and “you.” Plath distances herself from the tree and merges with it. She therefore creates the multiple voices of the poet’s psyche.

Structure
The poem comprises fourteen stanzas of three non-rhyming lines each; a structure characteristic of Plath. This, like many of her other poems, is a first person monologue in free verse, with terse lines of unequal length reflecting the meaning and emotions of the poet.

Language and Imagery
Sylvia Plath’s poetry is usually dense and often obscure. She uses vivid and imaginative imagery that can be interpreted in multiple ways. Here, she conveys meaning through complex, wide-ranging and disparate ideas, rather like flashing camera shots — elm, a horse, poison, dreams etc. Random as they may seem, the images overlap and repeat themselves cleverly so, for example, the violence of the broken tree in stanza 7 is echoed by the murderous face in stanza 13; the horse in stanza 4 is repeated in stanza 5; the bird in stanza 10 reappears in stanza eleven. These serve to draw the poem together so that Plath paints a terrifying picture of depression, despair and rage, digging deep into emotional depths.

See Sylvia Plath A Critical Guide, Tim Kendall Faber and Faber