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;