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<Version> versionList = versionManager.GetVersions();

      Version defaultVersion = versionManager.GetDefaultVersion();

      IEnumerable<Version> publicVersions = versionList.Where(
        version => version.GetAccessType() == VersionAccessType.Public);
      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;
  }
}