I think the family tree model of linguistic history is not very useful for English. Saying English is Germanic to the exclusion of everything else is not very useful.
The family tree model seems to assume that every language has only 1 direct ancestor. It seems to have been inspired by phylogenetic trees in biology. In phylogenetics, single-parent trees work fine because distantly related species can't breed with one other. By contrast, different languages borrow features from one another all the time. It could perhaps be useful for some languages, but not for English. I reckon.
The family tree model seems to assume that every language has only 1 direct ancestor. It seems to have been inspired by phylogenetic trees in biology. In phylogenetics, single-parent trees work fine because distantly related species can't breed with one other. By contrast, different languages borrow features from one another all the time. It could perhaps be useful for some languages, but not for English. I reckon.