You have the burden of proof to support your claim. I've already shown by scriptural context that my interpretation is correct.No it's not. It is sin in general.
The sin of unbelief is certainly the root of sin in general, isn't it? After all, didn't the serpent convince Eve not to believe God? Isn't any sin of disobedience grounded in lack of faith that God's way is best? Tell me, if a person commits adultery, are they in a state of belief that God's command "do not commit adultery" is good for them? If a person bows before an idol, are they actually believing that YHWH is the only true God? If a person disregards God's command, are they actually believing God then?
You need to explain how any sin is based on faith rather than unbelief. But the writer of Hebrews is getting to the heart of the matter, which is unbelief, so stated in 4:11. And we know it starts with Christ, as he explains in ch. 1. And since the whole epistle is about faith in Christ, you will need to show by exegesis that "sinning willfully" means any sin at all (or "sin in general"). What does the context tell us?