fstree: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/fstree - from package: python-fs

You may install the required package with command apt-get install {package}
Error in other languages:
fstree: bevel nie gevind nie
fstree: comandă negăsită
fstree: comando não encontrado
fstree: commande introuvable
fstree: command not found
fstree: käsku ei ole
fstree: không tìm thấy lệnh
fstree: komanda nerasta
fstree: Kommando nicht gefunden.
fstree: kommandot finns inte
fstree: komut yok
fstree: nie znaleziono polecenia
fstree: níor aimsíodh an t-ordú
fstree: no se encontró la orden
fstree: no s'ha trobat l'ordre
fstree: opdracht niet gevonden
fstree: parancs nem található
fstree: perintah tidak ditemukan
fstree: príkaz nenájdený
fstree: příkaz nenalezen
fstree: команда не найдена
fstree: командата не е открита
fstree: 命令找不到
fstree: コマンドが見つかりません