The first time I leaned back on the tree tether at height felt like a leap of faith. Same went for getting into different shooting positions. But 15 minutes of messing around and I was comfortable. My two suggestions, one is obvious.
Practice (obvious one). First a foot off the ground to get use to the saddle, bridge, tether, and mounting and leaning on the platform. Then practice using two sticks with your lineman’s belt. Two because your not to far off the ground with two sticks but can practice transitioning from the top stick to the platform. The most likely time to fall is this transition from onto or off the platform. I am tied in with the tether and lineman’s belt for this step getting on or off the platform. Practice getting the platform strapped down sturdy and stable.
Be deliberate. Every single step of the process be deliberate and focused on what you’re doing every time you climb. It will become second nature with repetition but still be focused.
I guess a third thing I would suggest is ease into putting tension on the tether. Don’t take the lineman’s belt off until you confirmed tether tension and hold.
Enough practice at low heights may alleviate (most of) the concern once 20 feet up. How much just depends on your tolerance for it.
These days tree stand platforms are getting pretty darn mobile in their own right. If the saddle thing just seems to much maybe look at ultra mobile tree stands. I’m thinking about adding one to the arsenal. But I really like how a saddle allows you to hide behind the tree, shoot while standing (without transitioning from sitting), and more shooting positions (though the amount of movement needed makes some positions difficult to get into).