Adventure game

Hi guys,
can anyone tell me how to handle missions in an adventure game. i'm gonna do a game in which missions will change dynamically based on the stats of the player. so how to keep track of missions and sub-missions; say for ex the player is in a main mission, to finish the main mission he has to do some sub-missions based on the output of the sub-mission he has to proceed.More Clearly See the attachment.
https://sites.google.com/site/tweettestsite/test_swf
I feels that i can handle these things using trees still i want to know is the approach reliable.If u have any suggestions always welcome.

Thanks in advance