Draft new `tree` API #52

Job	Run time
cross-compile-ios (macos-latest, 1.60.0, aarch64-apple-ios)	2m 15s
test (ubuntu-latest, 1.60.0)	1m 56s
cross-compile (ubuntu-latest, 1.60.0, aarch64-fuchsia)	1m 51s
test (ubuntu-latest, stable)	18s
cross-compile (ubuntu-latest, 1.60.0, aarch64-linux-android)	1m 48s
test (ubuntu-latest, beta)	18s
cross-compile (ubuntu-latest, 1.60.0, i686-pc-windows-gnu)	1m 50s
test (ubuntu-latest, nightly)	18s
cross-compile (ubuntu-latest, 1.60.0, i686-unknown-freebsd)	1m 59s
test (macos-latest, 1.60.0)	2m 4s
cross-compile (ubuntu-latest, 1.60.0, i686-unknown-linux-gnu)	1m 49s
test (macos-latest, stable)	21s
cross-compile (ubuntu-latest, 1.60.0, wasm32-unknown-unknown)	1m 48s
test (macos-latest, beta)	19s
cross-compile (ubuntu-latest, 1.60.0, x86_64-apple-darwin)	1m 52s
test (macos-latest, nightly)	19s
cross-compile (ubuntu-latest, 1.60.0, x86_64-unknown-redox)	1m 50s
test (windows-latest, 1.60.0)	2m 3s
test (windows-latest, stable)	58s
test (windows-latest, beta)	36s
test (windows-latest, nightly)	35s
	27m 7s

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