I am far from a professional .But just looking at that tree made me nervous Glad it is down without any bad results . And I agree with the above comment .

it came down sideways because you had to lift over the chunk of the notch you didn't remove and in doing so you broke your fiber making your hinge

that chunk of un-removed notch "steered" it sideways

And advice is what he got. If you really want to learn, for the novice, there are logger training courses available called , Game of Logging level 1 & 2. Teaches how to use the Open Face Notch technique, in NY workers compensation ins. Companies are requiring it now.
Nothing wrong with the Humboldt notch, but for the novice , open face and bore cutting ,is probably the way to go.

Is this a good time to mention the sights on a saw?

Stihl has a pretty decent Youtube series on how to fall a tree, as does Husqvarna. While watching videos is not a replacement for in person training, at least it will start to equip you with the knowledge to use your saw safely. As has been pointed out if the face cut (notch) is not correct it will only get worse from there and once you lose your holding wood that tree can go anywhere and you have no control over it. I am glad you got the tree down and didn't get injured but don't plan on being as fortunate in the future, it is dangerous felling trees even when you do it right.

This is a great video demonstrating 8 ways to fell a tree including using the sights on the saw to aim the cut. Well worth the time to watch.

Guilty of Treeson
https://youtu.be/nLIEYvHMS8U

I been looking at tree falling on youtube because I have a few big trees like that that has to come down.

here is the fellers safety training

https://www.worksafebc.com/en/resou...ideo-series/introduction-1-of-17?lang=en

if you want videos where the process is well explained Bucking Billy Ray Smith on youtube does a good job of explaining process and you will start to understand how important that under cut and hinge are

on the big ones especially if I have a bit of a lean I am going with , I get get my undercut in. I like a Swensen undercut , then I bore cut leaving my hinge and the trigger.

Glad ya got her down. That had me biting my nails!

Not much hinge wood left, however, it did rotate exactly how it should of considering the hinge...such as it is.

Little exaggerated, but you get the idea. I like the > notch and then cut up above on the back side at an angle. If you miss judge the balance the tree will come back some on the angle back cut and you notice it quicker(for me anyway). That’s when I stop and get a wedge to hold it, then a rope up high and pull.

I've been professionally logging since 1982 , Here is my advice if you can find a logger training class near you go take the cutter training class. Most states have them usually in the fall, it's better than getting killed or ending up in a wheelchair. Every year guys that know what there doing get killed.

^^^^^^
I know just enough about falling to be dangerous.

Soooo many folks are lucky.Every tree has a catastrophic potential.
Seen many get away unscathed, and others ..... not so.
A friend had been cutting wood for 40 years, every year (not commercially)
Cut a big limby white oak, fell it downhill the way it was leaning. It cleared the stump and went over exactly as expected.
The large lower limbs hit the ground, folded under the trunk like a spring then catapulted the whole tree up the hill over 10' and crushed him.
I watch for that every time I cut anything.

I had a widow maker come out of the tree behind me hit my hard hat and pin me to the ground

wasn't even the tree I was cutting on

watch out cutting after storm damage

My hard hat saved me any serious injury , since the fork hit my hard hat then my shoulders and took me to the ground just bruised shoulders and back

I was pinned on my saw bar against the ground and was able to shut it off

buying a chainsaw does not mean you should be cutting timber, I was 2 years learning from an experienced logger, could go down the list of what was wrong with that cut, glad it worked out for ya, but don't get comfortable with it.

I have one more big tree to Cut,, I will show pics of the hinge. I'm going to show you that the first tree was a fluke.

Please don't kill yourself

No I wont.

[/quote]
Not much hinge wood left, however, it did rotate exactly how it should of considering the hinge...such as it is.[/quote]
What Waggler said. They will pull toward the side that has the most wood holding. If you have enough trees to practice on it’s fun to notch them and then make them pull 90° as they fall. Just make sure the tree is solid and not hollow when trying that. It is dangerous but no one was born knowing how to fall trees, takes mistakes to learn.