debtree: command not found

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/debtree - from package: debtree

You may install the required package with command apt-get install {package}

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