get_node_manager
Description:
Get the TreeManager which created node in 
        this
Parameters:
| this | a Tree | 
| node | a TreeNode present in this | 
Returns:
| the TreeManager, or  | 
Get the TreeManager which created node in 
        this
| this | a Tree | 
| node | a TreeNode present in this | 
| the TreeManager, or  |