You are lucky to have a BRT that has lots of zig-zag low on the trunk. Most of them are left alone when young and become "Too Tall Jones" which sets the character in stone. That is very hard to overcome. To grow the tree in proportion, you need to keep in mind that every leaf contributes to increase in growth of the trunk below it, and o
nly below the branch where it grows. To state it conversely: Each ascending level needs to have fewer leaves than the previous level in order to grow less than the lower level. You have 8 distinct zig-zags, with only one section, 7 to 8, that is longer and the same diameter than the one immediately below it. This is golden. You need to stop growth above #8 for as long as it takes to become thinner than the diameter of #6 to 7. (BRT has a tendency to grow branches that are not round, but instead are oval. This leads to being seen as thinner from one view than they really are, or seen as thicker if viewed from 90° or the wider view of the oval giving an impression of inverse taper. The tree twists as it grows (nobody knows why) so it can have perfect taper and still look like it has inverse taper from one view or another. Yours looks very good. Luck of the draw!
Anyway, if you have 50 leaves one branch #1, you need 45 or 40 on #2 to maintain taper between #1 to #2, and then 35 to 30 on #3, 30 to 25 on #4, 25 to 20 on #5, 20 to 15 on #6, ad infinitum. You could shorten #5.5, 6 & 8 to dotted lines and limit growth there, and hope for some branches at #2, 3, 5 & 7. The bigger the difference in the number of leaves between the ascending branches, the bigger the difference in the size of the trunk between them. (You should choose to keep either 5.5 or 6 and eliminate the other or eventually two branches at one point will contribute to a swollen node and inverse taper.) The branches should radiate like a spiral staircase ascending the trunk with each shorter and thinner than the one below it and rotated 130° about the centerline of the trunk. The tippy-top should favor new, thinner branches over thicker, older branches, as zig-zag as possible, and radiate like a snowflake, but horizontally. (This whole paragraph is an ideal formula. It won't grow like that, so wire is necessary when and where needed. Do the best you can with what actually grows.)
Grow it in a pot the same size & shape as you want it to ultimately be the finished size. Repot every year in early summer. Feed only in the growing season in the presence of good light.
