[Molecular-evolution] A question of SOWH Test

[Xian Wang]

hi, 
    I am a green hand to paup and phylogenetic analyses. I have to do SOWH test on
my own data, and I found a detailed instruction of how to do it witten by Jon
Anderson, Nick Goldman, and Allen Rodrigo(Guidelines for performing the SOWH Test
). 
    I have got paup and Gen-Seq on my computer. Also I have learned how to do
simple analysis using these two tools.
    My question is that how could I get the null hypothesis tree using paup? Or
does null hypothesis tree are user-defined? I am totally confused. I can only got
ML tree using paup and modeltest.
    Can anyone help me? Thank you very much! 
                                                                Grace