A Girl

Ezra Pound

The tree has entered my hands,
The sap has ascended my arms,
The tree has grown in my breast-
Downward,
The branches grow out of me, like arms.

Tree you are,
Moss you are,
You are violets with wind above them.
A child - so high - you are,
And all this is folly to the world.

The title of this poem, ‘A girl’, caught my eyes. When I first read it I couldn’t understand it easily. I think the tree is a metaphor of a child who is growing. The author describes how a tree grows as how a child grows.
I don’t understand the last part. ‘And all this is folly to the world’. Is the author criticizing the world? Why the violets and moss randomly came out? Why the title is A Girl? Can’t it be a boy?