Open the split with pins, force glue in, wrap with a binding twine or rubber band to clamp it together while it dries. Allow to fully dry before taking off binder. Take off excess glue carefully. If you use steel wool or sandpaper be very careful not to round the edges. Use 600 or 800 grit for coarse work, 1000 to 2000 for fine work. Go really slow - you do not want to remove any bamboo, but you can go into the varnish. Get some tan silk (or nylon) rod thread, size A or so, and do an "invisible wrap" over the repair to reinforce it. Varnish the invisible wrap and you are done.
If that sounds a bit much, look up bamboo rod makers in your area. They can fix it. Fly shops may also give youa lead on people who do bamboo rod repair.