def display_arbre(villes, arbre, mult=1, screen=None, pygame=None):
    """
    dessine le graphe de poids minimal dꧩni par arbre
    """
    if mult == 2:
        color = 0, 255, 0
        li = 4
    else:
        li = 1
        color = 0, 0, 255
    for i in range(0, len(villes)):
        for j in arbre[i]:
            v = villes[i][0] * mult, villes[i][1] * mult
            vv = villes[j][0] * mult, villes[j][1] * mult
            pygame.draw.line(screen, color, v, vv, li)
