Shoetrees are objects that you put inside your shoes to help them keep their shape when you're not wearing them.
Shoetrees are helpful for keeping your shoes nice and neat.
Examples:
I use shoetrees to keep my shoes looking good.
Do you have shoetrees for all your shoes?
My dad's shoetrees are made of wood.
The shoetrees make my shoes look like they're standing up straight.
I have special shoetrees for my fancy shoes.
The shoetrees are like pillows for my shoes.