If it's spurless I'm definitely spending all the time it takes to preset a line. In that case I would also just just walk up the rope to the tip. I rarely go underneath unless it's only a slight lean and swinging to the upside won't be too much of a hassle.Best way is to preset a line from the ground to the tip of the leader with a second line and ropewalk that out to the tip of the leader
If spurless and no preset line can be installed it can be a painfully laborious sling-step and sling-grip ascent.
I find this happens especially on topped trees where the branches become leaders and are heavy leaners but also easily snap-able as overextended in some cases so having progressive rope tie-ins(similar to dog-bones when rock climbing) can be helpful as far as safety or confidence goes.
Some climbers stay on top all the way but in small diameter stuff with few side branches I often go underneath and use my lanyard using arms similar to hip-thrusting to advance, when high enough tie a rope running-bowline style then a wrap around the leader, take a step back down, then haul myself on top of the branch again. Sometimes use a wrap with my lanyard if bark too slippery or angle too steep.
If spurless can be a painfully laborious sling-step and sling-grip ascent.
Best way is to preset a second line from the ground to the tip of the leader and ropewalk/hand ascender that out to the end/tip of the leader
Would like to hear others techniques