These trees, unless you're working with collected European native stock, are extremely poor bonsai candidates, but they can be done. This was the first outdoor bonsia species I worked on 15 or so years ago. I still have those trees, so I have a weakness for them
They are a pain to style and need to have branches that grow bolt upright yanked down to 90 degrees or lower to be convincing. That usually means splitting the branch at the trunk union --with an incision along the top or bottom of the branch at the trunk with a sharp knife---and pulling the branch down and wiring it into place.
Thinning out the thick top growth and opening up the interior of the crown is a necessity with these kinds of trees. If you don't, the interior branching dies off. I remove about 50 percent of all interior crown branching....Good luck
