MD without knowing specifics I can only guess. First you should have put the stand up at an angle that allowed the top section to get a " bite" then about half way up you shouldve strapped the ladder to the trunk of the tree before going any higher. Only after that should you have gone up to secure the platform. Also, what angle did you have it at? ANY ladder is designed to be basically straight up and down so that the ladder can hold the weight in a vertical direction vs bending inward or outward.

I too bought a HV 2 man ladder lastyear with an additional 4' extension. This came with an additional metal brace that tied the ladder in to the trunk and allowed you to tighten the ladder up snug so that it doesnt move while climbing or using the stand.

Good luck and be careful in those things!
RA