Get names of root directories in an array in bash

I have a list of files which are stored here:

FILES_CHANGE=(git diff --name-only --cached)

This retrieves for example:

test.txt
home/a/c/test.sh
test/s.cpp

I need to get only the occurrencies with root directory name. In the example above would be:

home
test

How can I do this with bash? Any possibility to single line it with sed?

>Solution :

Another option using cut:

git diff --name-only | cut -d '/' -f1

Local example:

$ git --no-pager diff --name-only
src/API/Api.php
src/Commands/Data/Data.php
$
$
$ git  diff --name-only | cut -d '/' -f1
src
src
$