A natural tree cavity carved by a woodpecker

We’ve put up bluebird nest boxes since we first moved here in 1970. I’m thinking that man-made boxes mounted on posts don’t look good in the natural landscape. I’m exploring ways to create cavities similar to the ones that birds would use if we weren’t here. The cavity in this picture was carved by a woodpecker. I want to try to create some that are carved with a chain saw but still look natural.