var tree = {
	doExpand: function(obj, type, lminus, tminus, lplus, tplus) {
		var image = "";
		if(obj.parentNode.nextSibling.style.display == 'none') {
			obj.parentNode.nextSibling.style.display = '';
			switch (type) {
				case "L": image = lminus; break;
				case "T": image = tminus; break;
			}
		} else {
			obj.parentNode.nextSibling.style.display = 'none';
			switch (type) {
				case "L": image = lplus; break;
				case "T": image = tplus; break;
			}
		}
		obj.style.backgroundImage = 'url(' + image + ')';	
	}
}