The Kangaroo Special BMX dirt bike is composed of nine major subassemblies:

frame, seat assembly, rear wheel assembly, chain, front wheel assembly, fork, brake assembly, handlebar assembly, and pedal-crank assembly. The handlebar assembly consists of the handlebar, post, and two handlebar grips. The front wheel assembly consists of a tire, a tube, a rim, thirty-six spokes (20 mm), and a front hub assembly.

The front hub assembly is composed of the front hub, two bearings, two bearing re-

_tainers, an axle, and four axle nuts. The pedal-crank assembly is composed of a crank, a sprocket, two bearings, a bearing retainer, a nut, and two pedals.

Construct a product structure tree, showing the entire composition of a Kangaroo Special one level below the end product, and extend the composition of the front wheel assembly as far as possible.