The mtree_mod.c file has three pv param settings that is not documented in the README https://kamailio.org/docs/modules/devel/modules/mtree.html
* pv_dstid * pv_count * pv_weight
I see that pv_dstid and pv_weight is set in the code.
I can't really guess what they are, so I can't add docs myself...