TreeManager.with_func
Description:
[ CCode ( has_construct_function = false ) ]
[ Version ( since = "4.2" ) ]
public TreeManager.with_func (TreeManagerNodesFunc update_func)
  [ Version ( since = "4.2" ) ]
public TreeManager.with_func (TreeManagerNodesFunc update_func)
Use this method to create a new TreeManager if it's more convenient than 
      subclassing; all is needed is the update_func function which is responsible for creating or updating the children nodes of a 
      specified TreeNode.
Parameters:
| update_func | 
           the function to call when the manager object is requested to create or update its list of TreeNode nodes  | 
      
Returns:
| 
           a new TreeManager  |