Who knows? Trees grow how they want. You could top the tree now at the top or a foot down (Or even lower as long as there is still leaves down below your prune) and it will start branching there.

Your mandarin seedling tree is being dominated by the apical bud. Top the tree at 2.5 to 3 feet and the tree will quickly begin to grow many side branches.

citrus trees grown from seed rely on their node count to trigger bearing fruit. if you prune it, you risk delaying the fruiting

If you don't top the tree so that it will grow like a tree with side branghing, your tree will keep growing straight up, become weak (if not already) spindly and unable to support itself. Its very sad to see a container tree needing a stick to support the tree so that it can stand.