git-write-tree man page
git-write-tree — Create a tree object from the current index
git write-tree [--missing-ok] [--prefix=<prefix>/]
Creates a tree object using the current index. The name of the new tree object is printed to standard output.
The index must be in a fully merged state.
Conceptually, git write-tree sync()s the current index contents into a set of tree files. In order to have that match what is actually in your directory right now, you need to have done a git update-index phase before you did the git write-tree.
Normally git write-tree ensures that the objects referenced by the directory exist in the object database. This option disables this check.
Writes a tree object that represents a subdirectory <prefix>. This can be used to write the tree object for a subproject that is in the named subdirectory.
Part of the git(1) suite
git(1), git-commit-tree(1), git-read-tree(1).