I've found myself in the situation where I've chiseled a slight outward angle into my mortise, so when I insert the tenon, it is snug at the top, but I can wiggle it forward and backwards a bit with the tenon parallel to the plane of my body.
Should I try to glue in some thin wedges?
Or should I make a paste of wood glue and sawdust and layer it on the inside of the mortise a bit, then re-chisel it to be vertical? Would that have any strength, and would glue adhere to it once the tenon is inserted?