I'm not a structural engineer but I'm in agreement that the wall is needed. The reality is you're in a bad place. The builder has the upper hand. He's already profited from the work performed and has , or can, file a lien on your property. If you sue him, he's likely to disappear and open up under another name.
Be calm. Hire another engineer if need be. Try to work with your builder otherwise you could have a large concrete bowl down by those trees.
Be calm. Hire another engineer if need be. Try to work with your builder otherwise you could have a large concrete bowl down by those trees.