altree: 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/altree - from package: altree

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