The id of the tree object(s) to be read/merged.
-Merging
+MERGING
-------
If `-m` is specified, 'git read-tree' can perform 3 kinds of
merge, a single tree merge if only 1 tree is given, a
have finished your work-in-progress), attempt the merge again.
-Sparse checkout
+SPARSE CHECKOUT
---------------
"Sparse checkout" allows populating the working directory sparsely.