I think the way I've shown it is possibly the best way. I just leave the loop in the carabiner. Then wrap the loop through the platform and hook the loose end back into the carabiner. This does 3 things: 1) eliminates need for a larkshead - which lowers break strength. In fact, you might even gain strength because the rope is doubled over, similar to a soft shackle 2) makes is so that you can't lose the loop while walking in, and 3) shortens the distance between the platform and the buckle, which sets the minimum distance you can place a step on that side. If you were to larkshead, or even splice the loop directly onto the platform, you wouldn't be able to place a step very close to the platform. On a small-medium sized tree, that might mean not having a step exactly where you'd want it.
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