How can I set the Matrix Type to Bipolar when importing from a TXT file?

As the title states, how can I set the Matrix Type to Bipolar? I've been trying several combinations, but it doesn't seem to set anything. I'm familiar with the basic tags such as [[Block]], etc. I would have thought the tag / code would be [[Matrix:MatrixType:Bipolar]] or something of the sort.

I'll be eternally grateful if someone can point me in the right direction. (I've looked over the documentation several times but there's no explicit code for the matrix type)