Getting all the group for a particular web

public IList<string> GetAllUserGroups(string url)
{
    IList<string> groupList = new List<string>();

    using (SPSite site = new SPSite(url))
    {
        SPGroupCollection groups = site.RootWeb.SiteGroups;
       
        foreach (SPGroup g in groups)
        {
            groupList.Add(g.Name);
        }
    }

    return groupList;
}