Many larger imported bonsai Ficus are in fact not one tree but in reality many smaller figs that have been allowed to fuse or graft together. This is done to utilize inferior stock that can be rapidly converted into more mature and finished trees or to correct for missing branches, roots or a small trunk.
Obtain or grow multiple small trees, preferably cuttings from one tree. In that way they will be alike in all respects; bark color, leaf size and shape will be the same. Do not use random seed grown Ficus as their bark color and other characteristics will vary and the final creation may look "unusual". The trees are removed from their pots and all roots are kept intact. Branches that interfere with the positioning of the trees next to each other are removed. Trees are secured to each other with plastic wrapping twine. Remove any large roots that interfere with trunk placement and place all the roots into the soil. Make sure to keep the roots moist during this process.
Pot the trees without doing any shaping or trimming, other than that required to get the trees next to each other. Do not plant them into a small bonsai container but one that will allow them to grow as quickly as possible. Allow the trees to grow vigorously and do not trim any growth off the tree(s). Over 12-18 months the trees will grow and fuse into each other. Some of the smaller trees may die in the center of the grouping but that is fine as the dead and live trunks will fuse becoming the trunk of the new larger tree.
Shaping the trees and wiring is done only after the trees are well along in their fusion. Do not fertilize for two to four weeks after potting and keep the tree out of direct sun and wind for a few weeks. After that, the trees can be moved to stronger light and fertilized.
After 12-24 months of uncontrolled growth, you can inspect the tree by undoing the tape to see if the fusion process is going well. The tape can be reapplied if the the trees appear loose and need more fusion. Once the trees fuse the plastic tie can be removed and the braches shaped with wire. Use each little tree's apex to represent one branch in the finished tree.
As time goes by the trunks will fuse together even more and the roundness of the original trunks will fold into the trunk's overall shape.
The creation of a fused style fig is an extremely easy manipulation. Young inexpensive Ficus can be propagated or purchased and fused. With this simple technique a bonsai can be created from rather unexciting young trees.