I still don't see it.
IMO to make modifies way because alternative parallel structures could involve:
way to eat....way to serve.....way to order....way to picture....etc
none of which affects the noun sundae,
The diagram appears to reflect that since down branches located immediately before the other nouns clearly indicate traditional adjectives.
It seems that because all of the infinitives that you're using:
all refer to sundae, then they pertain to sundae. They cannot be used independently of sundae, as in:
way to make is. . . to make what?
way to eat is. . . to eat what?
way to serve is. . . to serve what?
way to order is. . . to order what?
way to picture is. . . to picture what?
To be honest, I had to look up the use of verbs as adjectives--in this case the infinitive form as a relative clause--after I read this thread, and still wasn't sure until I diagrammed it.