Add ASV for datatree.from_dict (#9459)

Author: Illviljan

asv_bench/benchmarks/datatree.py

@@ -0,0 +1,11 @@
+import xarray as xr
+from xarray.core.datatree import DataTree
+
+
+class Datatree:
+    def setup(self):
+        run1 = DataTree.from_dict({"run1": xr.Dataset({"a": 1})})
+        self.d = {"run1": run1}
+
+    def time_from_dict(self):
+        DataTree.from_dict(self.d)