This method computes the final tree hash used on the CompleteMultipartUploadRequest from the tree hashes of
the individual part uploaded.

C# |
public static string CalculateTreeHash( IEnumerable<string> partsTreeHash )

- partsTreeHash (IEnumerable<(Of <(<'String>)>)>)
- The list of tree hashes for the individual parts.

The tree hash that can be used to set the the Checksum property.