What is formed when any two branches diverge in a phylogenetic tree? a node a lineage a population a root a module?

The answer is a lineage

A phylogenetic tree demonstrates, visually, the relationships between species and their common ancestry to depict evolutionary trend. This tree is based solely on similarities and differences in phylogeny (genetically and phenotypically) of organisms.

Therefore a branch portrays divergence in phylogeny of two species from a common ancestry thus forming two different lineages.