Problem with solid bodies

Hi all,
I have a problem in my tree displaying Solid bodies.
I make a surface, something very basic, like a square. My surface appears in the folder "Surface Bodies" so no problem here. I click on thicken. Set the thick on 1mm. I guess I made a solid that way but in my tree I don't have any "Solid Bodies", nothing.
Is that normal?

Thank you very much.