There is no industry “standard.” Everyone writes and formats their treatments in a format that is comfortable them. That said, they are typically written in a first-person, plural (“We see a house,”) or second-person, singular (“You see a house”) so that the treatment emphasizes the guest experience. They are also segmented by room or scene, and will have technical and logistical information for that room (talent, audio, effects, etc.).
Here are some I’ve written:
Haunt – Imaginary Vagabond