Weird donut-shaped pus on sole of foot

Does anyone know what this is called? It seems to be pus around a dark indention. There is a quarter-sized area of swelling around the pus. It hurts if i push on it, and walking is painful. This developed over the past week and a half. I think this began with me stepping on a sharp pebble, and i did not notice it breaking the skin. I looked up wart, corn, abscess, infection, etc, and I could not find any images to match this. If you know what it is, how do i treat it? I have tea tree oil on it currently. I appreciate any help. Thank you.




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