Removing a tree node doest not require the 'id' value. Here is the extended method to remove all the tree nodes.
$.extend($.fn.tree.methods, {
	removeAll:function(jq){
		return jq.each(function(){
			var roots = $(this).tree('getRoots');
			for(var i=roots.length-1; i>=0; i--){
				$(this).tree('remove', roots[i].target);
			}
		})
	}
})
Calling 'removeAll' method will remove all the tree nodes.
$('#tt').tree('removeAll');