Add static tree support for treevalue

[HansBug]

Well, though this is called "tree" as well, but I tend to treat it as another kind of data structure, like segment tree.

Its properties:

• You can store (or called manage) something on the non-leaf nodes
• The structure is fixed, including tree structure and max capacity of nodes

Based on this, pickle.loads and picke.dumps can be optimized because this serialization can be directly performed on the data of root node.