TreeSelect implement Tree as popup panel which use title as the display
text.
To follow the Select definition (label as display text), TreeSelect
internal convert the prop label into title to the Tree component (but
will follow if title is set).
ref:
https://github.com/react-component/tree-select/blob/master/src/Select.js
x#L44
* Unify name of ReactNode type in document
* Lowser all string type name
* Lowercase all number type name
* Lowercase all boolean type name
* Unify array type
* Lowercase all object type name
* Unify mutilple types