Add `TreeStyle` to PSTree #85

Job	Run time
build	1m 51s
test (PS-5.1, 5.1, windows-latest)	1m 1s
test (PS-7_Windows, 7, windows-latest)	59s
test (PS-7_Linux, 7, ubuntu-latest)	40s
publish	0s
	4m 31s

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