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: convert.m
    path of file: ./repos/CBIG/external_packages/matlab/non_default_packages/cifti-matlab-WashU-gradient/@xmltree
    
    the code of the file until where you have to start completion: function s = convert(tree,uid)
% XMLTREE/CONVERT Converter an XML tree in a structure
% 
% tree      - XMLTree object
% uid       - uid of the root of the subtree, if provided.

    
function s = convert(tree,uid)
% XMLTREE/CONVERT Converter an XML tree in a structure
% 
% tree      - XMLTree object
% uid       - uid of the root of the subtree, if provided.
%             Default is root
% s         - converted structure
%__________________________________________________________________________
%
% Convert an XMLTree into a structure, when possible.
% When several identical tags are present, a cell array is used.
% The root tag is not saved in the structure.
% If provided, only the structure corresponding to the subtree defined
% by the uid UID is returned.
%__________________________________________________________________________
% Copyright (C) 2002-2015  http://www.artefact.tk/

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

% Exemple:
% tree = '<a><b>field1</b><c>field2</c><b>field3</b></a>';
% toto = convert(xmltree(tree));
% <=> toto = struct('b',{{'field1', 'field3'}},'c','field2')

%error(nargchk(1,2,nargin));

% Get the root uid of the output structure
if nargin == 1
    % Get the root uid of the XML tree
    root_uid = root(tree);
else
    % Uid provided by user
    root_uid = uid;
end