Sharon Saare tree sizes

Hey guys. I am completely unfamiliar with western saddles but there’s a Sharon Saare saddle on Craigslist I’m interested in that has a tree size of BHG. I can’t figure out what this means. Any ideas? I saw somewhere that the tree sizes start at A and go through G, but I can’t find reference to a combination of letters like this.


ETA received an answer...Stands for tree size B, HG is high gullet.