Final answer:
The underlined part of the sentence is a simile that compares the branches filling the sky to a giant umbrella.
Step-by-step explanation:
The underlined part of the sentence 'Trees grew overhead and their branches filled the sky like a giant umbrella,' is a simile.
A simile is a figure of speech that compares two things using the words 'like' or 'as.' In this case, the branches filling the sky are being compared to a giant umbrella.
This comparison helps create a visual image in the reader's mind of how the branches cover the sky.
Learn more about Simile