No, "piece of cake" is an idiom, not a simile. It means that something is very easy to do. A simile is a figure of speech that compares two things using "like" or "as," such as "as brave as a lion."
As soft as a cloud.
cow
You can get a birthday cake when it is your birthday.
you have a birthday cake
Bella's birthday cake was Pink.
Birthday surprises
One simile is... The smell of melting chocolate was like being reborn into a chocolate cake
She honored Michael Jackson with a cake on his 44th birthday.
Is it a birthday cake. If so, it is added to your account on your birthday.
The birthday cake originated in Greece as a yearly sacrifice to the gods.
The person having the birthday!