Analysis of A Nightmare

I dreamed that I was dead. The years went by:
The world forgot that such a man as I
Had ever lived and written: other names
Were hailed with homage, in their turn to die.

Out of my grave a giant beech upgrew.
Its roots transpierced my body, through and through,
My substance fed its growth. From many lands
Men came in troops that giant tree to view.

'T was sacred to my memory and fame
My monument. But Allen Forman came,
Filled with the fervor of a new untruth,
And carved upon the trunk his odious name!