Where does “traŭbo” come from?

traŭbo (Esperanto) comes from German traube, from Middle High German trūbe, from Old High German drūbo, from Proto-West Germanic þrūbō, from Proto-West Germanic þrubō, from Proto-Germanic þrubô, from Proto-Indo-European trup-ḗn ~ trup-nés, from Proto-Indo-European -ḗn — Derives nouns from roots.

traŭbo (Esperanto): grape