You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: copy.m
    path of file: ./repos/cifti-matlab/ft_cifti/@xmltree
    
    the code of the file until where you have to start completion: function tree = copy(tree,subuid,uid)
% XMLTREE/COPY Copy Method (copy a subtree in another branch)
% FORMAT tree = copy(tree,subuid,uid)
% 
% tree      - XMLTree object
% subuid    - UID of the subtree to copy

    
function tree = copy(tree,subuid,uid)
% XMLTREE/COPY Copy Method (copy a subtree in another branch)
% FORMAT tree = copy(tree,subuid,uid)
% 
% tree      - XMLTree object
% subuid    - UID of the subtree to copy
% uid       - UID of the element where the subtree must be duplicated
%__________________________________________________________________________
%
% Copy a subtree to another branch.
% The tree parameter must be in input AND in output.
%__________________________________________________________________________
% Copyright (C) 2002-2015  http://www.artefact.tk/

% Guillaume Flandin
% $Id: copy.m 6480 2015-06-13 01:08:30Z guillaume $


%error(nargchk(2,3,nargin));

if nargin == 2
    uid = parent(tree,subuid);
end