Resolution:
MTree/mtree is the C/Java class that represents the RV message to be transmitted over TIB.
In terms of RV, an mtree is simply a nested RV message of type RVMSG_RVMSG.

A RV message can be viewed graphically as a tree structure where the nodes are simple name/value pairs (MData) and the branches are nested RV messages (MTree).

Additionally, the use of MTree in Adapter SDK based application is not recommended SDK 5 and up, using these lower level class make their
application "non-portable" "non-upgradable", as SDK introduced messaging transports beyond RV.