usertrees: 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/lib/fastdnaml/bin/usertrees - from package: fastdnaml

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

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