How do I concatenate multiple files in multiple directories with their names?

I have multiple files that contain codes, and am trying to merge them in order to print it out. They spread out in multiple directories.

For example, I have directories like:

    root
   /   \
 dir1  dir2
 / \   /  \
s1 s2 s3  s4

which each contain files, to be concatenated into one text file.

Final output would look like:

Filename(its directory name)
content

Filname 2 (its directory name)
content 2

.
.
.

Filename n (its directory name)
content n

Can someone help me achieve this using command line?

Provided that "in order" means in your locale's collation order, you can use simple shell globs.

Ex. given

$ tree root
root
├── dir1
│   ├── s1
│   └── s2
└── dir2
    ├── s3
    └── s4

2 directories, 4 files

then

$ for f in root/*/*; do { printf '%s (%s)\n' "${f##*/}" "${f%/*}"; cat "$f"; printf '\n'; }; done
s1 (root/dir1)
Contents of file 1

s2 (root/dir1)
Contents of file 2

s3 (root/dir2)
Contents of file 3

s4 (root/dir2)
Contents of file 4

If you just need something quick'n'dirty and don't need that specific format, then you could use head with a number of lines that is larger than the known line count of any of your files:

$ head -n 100000 root/*/*
==> root/dir1/s1 <==
Contents of file 1

==> root/dir1/s2 <==
Contents of file 2

==> root/dir2/s3 <==
Contents of file 3

==> root/dir2/s4 <==
Contents of file 4