Couple of different questions here. One is on your cutting technique for falling trees - I will leave that mostly to others, but agree that cutting straight through, as in the photo, can be dangerous. One is the species of wood (I don't know).
As for different angles for different wood, the short answer is '
Yes'. Under controlled (read '
laboratory') conditions, it is possible to optimize chain angles for different species of wood, as well as for live ('green'), dead ('dry'), or frozen conditions, etc. As a practical matter, that is only an issue if the wood you cut is remarkably uniform - such as if you cut on a Christmas Tree plantation, or production cut southern yellow pine, etc.
Most of us cut a variety of different woods, so we look to find the best, '
all-around' angles, for general use. It can be time consuming and wasteful to frequently change these angles for different cutting conditions,
BUT, you can have different chain loops filed for different uses, and swap them out (analogous to swapping sockets on a ratchet wrench) as needed.
FILE ANGLES AND CUTTING PERFORMANCE
30° is the top plate angle ('A' in photo), and usually the 'general purpose' angle for most chains. This angle is sometimes changed to 25° for hard or frozen wood, and 35° for softwood.
The diameter of the file (<x>) should be appropriate for the chain pitch;
File tilt or 'down angle' ('B), usually 0° or 10°;
Height of the file ('C') affects the bevel of the top plate cutting edge, or 'hook'; and
Depth gauge setting ('D') this is typically 0.025" for general or hardwoods, but is sometimes increased for softwoods.
More info in books like the Oregon Maintenance and Safety Manual:
https://www.oregonproducts.com/pro/pdf/maintenance_manual/ms_manual.pdf
Performance can even vary between saws (!). So, if you want to experiment with different angles, I recommend having a few loops of chains, filed at slightly different angles. Swap the chains back-and-forth in the same wood, with the same saw, and see if it makes a noticeable difference to
you. Fun to try, and you can learn a lot.
Philbert