tree-ppuzzle: 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/tree-ppuzzle - from package: tree-ppuzzle

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

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