This lovely image was created specifically for the webcomic "Stand Still. Stay Silent" by Minna Sundberg. It is not intended to be a complete picture of Indo-European languages.
The comic is set in a post-apocalytic future in which only the Scandinavian countries still exist, precariously.
The family tree is meant to help readers of the comic understand the relationships among the languages spoken by the characters in the comic, including the fact that some of them understand each others' spoken languages, but other characters aren't able to communicate with each other.
The Old World referred to on the image is the world that existed before the fictional apocalypse. The caption on the image states that the purpose of this family tree is to show the Nordic languages' historical relationships with other languages that existed before Year 0, the year that the disaster happened, i.e. the present.
The purpose of sharing this image is to point out that language family trees could be presented more artistically than they usually are - as a diagram with straight lines only.
It is particularly interesting that Minna Sundberg, the artist, has used the size of branches and the clumps of leaves to represent the approximate number of speakers of each language in the present. Latin isn't on the tree because Latin isn't spoken as a native language today.
Sources: sssscomic.com; Mentalfloss.com