public override byte[] ToEsriShape()

{
  // export to binary xml
  string binaryXml = multipatch.ToBinaryXml();

  // import from binaryXML - methods need to run on the MCT
  Multipatch binaryMultipatch = MultipatchBuilderEx.FromBinaryXml(binaryXml);

  // xml export / import
  string xml = multipatch.ToXml();
  Multipatch xmlMultipatch = MultipatchBuilderEx.FromXml(xml);

  // esriShape export/import
  byte[] buffer = multipatch.ToEsriShape();
  Multipatch esriPatch = MultipatchBuilderEx.FromEsriShape(buffer);

  // or use GeometryEngine
  Multipatch patchImport = GeometryEngine.Instance.ImportFromEsriShape(EsriShapeImportFlags.EsriShapeImportDefaults, buffer, multipatch.SpatialReference) as Multipatch;
}