In a book I'm reading there is a question as following
Does it come in birch
Here is the situation:
But wait, there’s more! There are other particles besides these four and they all fall into columns as well. Each column looks exactly like the first column (with the same properties like charge and force interaction) except the particles in them have more mass.24 We call each of these columns a “generation,” and we’ve discovered three of these generations. You might immediately have some questions about our table of particles: Does it come in birch?
My question is what does that sentence mean? I have searched "come in birch" in dictionaries and google but there is no information about it.
Please explain to me.