public Version GetParent()

public void ReconcileAndPost(Geodatabase geodatabase)
{
    // Get a reference to our version and our parent
    if (geodatabase.IsVersioningSupported())
    {
        using (VersionManager versionManager = geodatabase.GetVersionManager())
        using (Version currentVersion = versionManager.GetCurrentVersion())
        using (Version parentVersion = currentVersion.GetParent())
        {

            //// Create a ReconcileDescription object
            //At 2.x - 
            //ReconcileDescription reconcileDescription = new ReconcileDescription(parentVersion);
            //reconcileDescription.ConflictResolutionMethod = ConflictResolutionMethod.Continue; // continue if conflicts are found
            //reconcileDescription.WithPost = true;

            //// Reconcile and post
            //ReconcileResult reconcileResult = currentVersion.Reconcile(reconcileDescription);

            // ReconcileResult.HasConflicts can be checked as-needed

            // Create a ReconcileOptions object
            ReconcileOptions reconcileOptions = new ReconcileOptions(parentVersion);
            reconcileOptions.ConflictResolutionMethod = ConflictResolutionMethod.Continue; // continue if conflicts are found
            reconcileOptions.ConflictDetectionType = ConflictDetectionType.ByRow; //Default
            reconcileOptions.ConflictResolutionType = ConflictResolutionType.FavorTargetVersion;//or FavorEditVersion

            // Reconcile
            ReconcileResult reconcileResult = currentVersion.Reconcile(reconcileOptions);
            if (!reconcileResult.HasConflicts)
            {
                //No conflicts, perform the post
                PostOptions postOptions = new PostOptions(parentVersion);
                //var postOptions = new PostOptions(); for default version
                postOptions.ServiceSynchronizationType = ServiceSynchronizationType.Synchronous;//Default
                currentVersion.Post(postOptions);
            }

        }
    }
}

public void ReconcileAndPost2(Geodatabase geodatabase)
{
    // Get a reference to our version and our parent
    if (geodatabase.IsVersioningSupported())
    {
        using (VersionManager versionManager = geodatabase.GetVersionManager())
        using (Version currentVersion = versionManager.GetCurrentVersion())
        using (Version parentVersion = currentVersion.GetParent())
        {

            //// Create a ReconcileDescription object
            //At 2.x - 
            //ReconcileDescription reconcileDescription = new ReconcileDescription(parentVersion);
            //reconcileDescription.ConflictResolutionMethod = ConflictResolutionMethod.Continue; // continue if conflicts are found
            //reconcileDescription.WithPost = true;

            //// Reconcile and post
            //ReconcileResult reconcileResult = currentVersion.Reconcile(reconcileDescription);

            // ReconcileResult.HasConflicts can be checked as-needed

            // Create a ReconcileOptions object
            ReconcileOptions reconcileOptions = new ReconcileOptions(parentVersion);
            reconcileOptions.ConflictResolutionMethod = ConflictResolutionMethod.Continue; // continue if conflicts are found
            reconcileOptions.ConflictDetectionType = ConflictDetectionType.ByRow; //Default
            reconcileOptions.ConflictResolutionType = ConflictResolutionType.FavorTargetVersion;//or FavorEditVersion

            PostOptions postOptions = new PostOptions(parentVersion);
            //var postOptions = new PostOptions(); for default version
            postOptions.ServiceSynchronizationType = ServiceSynchronizationType.Synchronous;//Default

            // Reconcile
            ReconcileResult reconcileResult = currentVersion.Reconcile(reconcileOptions, postOptions);
            if (reconcileResult.HasConflicts)
            {
                //TODO resolve conflicts

            }

        }
    }
}

public async Task WorkingWithVersions()
{
    await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
    {
        using (Geodatabase geodatabase = new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file"))))
        using (VersionManager versionManager = geodatabase.GetVersionManager())
        {
            IReadOnlyList<string> versionNames = versionManager.GetVersionNames();

            Version defaultVersion = versionManager.GetDefaultVersion();

            string testVersionName = versionNames.First(v => v.Contains("Test"));
            Version testVersion= versionManager.GetVersion(testVersionName);

            Version qaVersion = defaultVersion.GetChildren().First(version => version.GetName().Contains("QA"));

            Geodatabase qaVersionGeodatabase = qaVersion.Connect();

            FeatureClass currentFeatureClass = geodatabase.OpenDataset<FeatureClass>("featureClassName");
            FeatureClass qaFeatureClass = qaVersionGeodatabase.OpenDataset<FeatureClass>("featureClassName");
        }
    });
}

// Check to see if the current version is default.
// Works with both branch and traditional versioning.
public bool IsDefaultVersion(Version version)
{
    Version parentVersion = version.GetParent();
    if (parentVersion == null)
    {
        return true;
    }
    parentVersion.Dispose();
    return false;
}

public bool IsDefaultVersion(Geodatabase geodatabase)
{
    if (!geodatabase.IsVersioningSupported()) return false;
    using (VersionManager versionManager = geodatabase.GetVersionManager())
    using (Version currentVersion = versionManager.GetCurrentVersion())
    {
        return IsDefaultVersion(currentVersion);
    }
}

// Gets the default version.
// Works with both branch and traditional versioning.
// Note that this routine depends on IsDefaultVersion(), above.
public Version GetDefaultVersion(Version version)
{
    if (IsDefaultVersion(version))
    {
        return version;
    }
    else
    {
        Version parent = version.GetParent();
        Version ancestor = GetDefaultVersion(parent);
        if (parent != ancestor)
        {
            parent.Dispose(); //If the versioning tree is more than 2 deep, we want to dispose any intermediary versions
        }
        return ancestor;
    }
}

public Version GetDefaultVersion(Geodatabase geodatabase)
{
    if (!geodatabase.IsVersioningSupported()) return null;

    using (VersionManager versionManager = geodatabase.GetVersionManager())
    {
        Version currentVersion = versionManager.GetCurrentVersion();
        Version defaultVersion = GetDefaultVersion(currentVersion);
        if (currentVersion != defaultVersion)
        {
            currentVersion.Dispose(); // If we are not pointing to default, we want to dispose this Version object
        }
        return defaultVersion;
    }
}