Tree is weaker than Toyou because toyou is 2 overheat. The poison deals 10 hits of the same skill damage (1 hit per 0.5 seconds, 5 seconds poison). The initial tree hits 9 times, so 19 hits total. Multiply skill factor by 19 to get tree damage, it’s lower than 2x toyou.
Onymo 3 is very easy to skill, use the build of @Sloth , that’s the correct build.
Standard max water, max toyou, max yinyang, 1 greenwood, rest howling white tiger.
Variations drop several tiger points:
Drop 1 tiger point: psychokino must take fire fox level 1 to unlock attributes.
Drop 5 tiger points: high SPR onmyo may take genbu 5.
Toyou hits half on knocked down enemies, so turn off that attribute if you feel weak. Use heavy gravity + toyou on flying.