What is being compared to the unfolding bud in this poem?

Directions: Read the following poem to answer the given question.

UNFOLDING BUD            
One is amazed
By a water-lily bud
Unfolding
With each passing day

Taking a richer colour
And new dimensions
One is not amazed,
At a first glance,
By a poem,
Which is as tight-closed
As a tiny bud.
Yet one is surprised
To see the poem
Gradually unfolding,
Revealing its rich inner self
As one reads it
Again

Naoshi Koriyama