How to add sync marker to Animation Composite?

I’ve been implementing a basic locomotion cycle: Idle - WalkStart - WalkLoop - WalkEnd - Idle. I’m combining the WalkLoop and WalkEnd together into a new animation, as the WalkEnd animation is like the left foot touch the ground then idle pose, so when my character stop while having right foot touching the ground, it has bad transition. So I want to make the stuff into a new animation so I can fit the Sync Marker into it, as he can walk one more step to the left foot when I stop with my right foot. But the Animation Composite have no Sync Marker. I have tried recording the Animation Composite, but the output Animation’s Root Motion does not work properly (two original animation have root motion both). How can I fix the problem? Is there any alternative way to do this?