<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def MergeMessage( self, source, destination, replace_message_field=False, replace_repeated_field=False):
 """Merges fields specified in FieldMask from source to destination. Args: source: Source message. destination: The destination message to be merged into. replace_message_field: Replace message field if True. Merge message field if False. replace_repeated_field: Replace repeated field if True. Append elements of repeated field if False. """

    tree = _FieldMaskTree(self)
    tree.MergeMessage(
        source, destination, replace_message_field, replace_repeated_field)