I am talking about a tree of, say, six inch DBH and, a log stem off that tree of, say, nine feet long. When I do a stack of firewood, I sometimes use small trees (saplings?) as the runners to put the first layer of wood on. I saw someone on here had done what I am talking about and I wondered how he split the stems so that the crack propagates all the way down the log. If you did this, you'd get two runners instead of one.
Run your chainsaw down the length of the piece, not too deep. Then use some splitting wedges into the groove. Keep tapping unail it splits through. If the grain is twisted, you might need to use the saw to go all the way through. Good luck!
Same process splitting fence rails. Basically you start a steel wedge at one end, and get the split started, and then put hardwood or plastic wedges into the split until it separates. Research "rail splitting" or "riving" on Youtube.
Skinny log, just keep leapfrogging your wedges down the length. Fat log... This work really well on skinny or fat red oak.
When we split locust posts for rails we used the tip of the chainsaw to make a hole for the wedge. Pound it in till tight then move down the log a bit and repeat. The second wedge should loosen the first. Good quality steel wedges if you can find them.
