SharePoint isn't really that hierarchical, it is all based on flat lists. That being said let me show you some hierarchy:
- You can have related lists. So you could have task list 1 which references task list 2. Now could have One main task in task list 2 which is being referenced from multiple "sub tasks" in task list 1
- You can use the regular task list for "successors" of your tasks. It shows you a list box where you can choose which tasks are the successor of the current task and that way have hierarchy, you can't visualize this in e.g. a treeview though
- You could use the "task groups" content type which groups multiple tasks together so you could have one overarching task
- you could use folders and have tasks within these folders and based on your needed hierarchy you could nest the folders deeper
I don't really see how the Managed Metadata Service (MMS) helps you as you are talking about tasks - the MMS is for metadata which could be hierarchical. Say you have the metadata "color". Nested beneath that could be "green, yellow and orange". Under "yellow" you could have "bright yellow, light yellow, sun, egg" or something like that.