public HistoricalVersion GetCurrentHistoricalVersion()

public void ChangeVersions(Geodatabase geodatabase, string toVersionName)
{
    using (VersionManager versionManager = geodatabase.GetVersionManager())
    {
        VersionBaseType versionBaseType = versionManager.GetCurrentVersionBaseType();

        if (versionBaseType == VersionBaseType.Version)
        {
            Version fromVersion = versionManager.GetCurrentVersion();
            Version toVersion = versionManager.GetVersion(toVersionName);

            // Switch between versions
            MapView.Active.Map.ChangeVersion(fromVersion, toVersion);
        }

        if (versionBaseType == VersionBaseType.HistoricalVersion)
        {
            HistoricalVersion fromHistoricalVersion = versionManager.GetCurrentHistoricalVersion();
            HistoricalVersion toHistoricalVersion = versionManager.GetHistoricalVersion(toVersionName);

            // Switch between historical versions
            MapView.Active.Map.ChangeVersion(fromHistoricalVersion, toHistoricalVersion);
        }

        // Switch from HistoricalVersion to Version and vice-versa 
        // MapView.Active.Map.ChangeVersion(fromHistoricalVersion, toVersion);
        // MapView.Active.Map.ChangeVersion(fromVersion, toHistoricalVersion);

    }
}