I have ordered the most expensive one because everything is on ooooo.
I have ordered the most expensive one because OOO treats us.
"〇〇の奢りだから1番高いの頼んじゃったー"
最も高いもの the most expensive one
頼む、オーダーする order ここでは現在完了を使っています。
過去形にすると臨場感が失われるので、
～のおごり be on ~ 例文 Everything is on him. Everything is on Tom.
おごる treat
I have ordered the most expensive one because everything is on ooooo.
I have ordered the most expensive one because OOO treats us.
日本 
