git-rev-tree: 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 CentOS possible default full paths are:

/usr/bin/git-rev-tree - from package: mercurial

You may install the required package with command yum install {package}

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