function tree_open(branch, img_open, img_close)
{
	if(document.getElementById(branch).style.display == '')
	{
		document.getElementById(branch).style.display='none';
		document.getElementById('img_' + branch).src = img_close;
	}
	else
	{
		document.getElementById(branch).style.display='';
		document.getElementById('img_' + branch).src = img_open;
	}
}