My solution would be a fake birdhouse. It could be weatherproof and less conspicuous, and the hole on the front is a natural place to put a camera lens. (You might want to put a fake bird on top or something to dissuade actual birds.)

Assuming it’s attached to a tree, how would you power it?

If I _had_ to put it in a tree, PoE or solar+battery would probably work. In my tiny yard I could probably get away with a regular outdoor extension cord.

Seconded. Needs to have ~90 deg FOV, either good enough low-light performance or provisions for an IR emitter, option for a sound interface, POE, and put in a case that looks inconspicuous enough to hang on my wall in my home. AFAIK that doesn't exist and I wish it did. Being able to run an open source cctv system would be great, as the other option is typically running grey-market chinese non-upgradeable firmware.

Option 1: search ebay (or a similar retailer) for "IP65 transparent" to find box-shaped waterproof enclosures with clear lids. Arrange electronics to your satisfaction, with the camera looking through the lid. Many sizes, but looks nothing like a normal CCTV camera.

Option 2: Search for "CCTV housing" to find boxes that look like old-fashioned outdoor CCTV cameras. Fewer size choices, but less weird-looking.

I don't have any pre-built recommendations, but you can figure out some dimensions and find someone online who'd be willing to 3D print it for you.

Or you could find a machinist. That'll be fairly expensive, though.

Lastly, you could probably make it using supplies from Home Depot, like PVC pipes + fittings and PVC cement, maybe some gasket sealer for any holes you drill. Probably the cheapest option of these 3.

There are many, many 3d printable enclosures on thingiverse and elsewhere. I recommend still using a gasket and epoxying the enclosure.