The 'lines' property will be supported in next version. You can extend a new method 'showLines' to achieve this functionality. The 'showLines' method will also be added into next version.
$.extend($.fn.treegrid.methods,{
	showLines:function(jq){
		return jq.each(function(){
			var target = this;
			var t = $(target);
			var opts = t.treegrid('options');
			if (opts.lines){
				t.treegrid('getPanel').addClass('tree-lines');		
			} else {
				t.treegrid('getPanel').removeClass('tree-lines');		
				return;
			}
			
			t.treegrid('getPanel').find('span.tree-indent').removeClass('tree-line tree-join tree-joinbottom');
			t.treegrid('getPanel').find('div.datagrid-cell').removeClass('tree-node-last tree-root-first tree-root-one');
			var roots = t.treegrid('getRoots');
			if (roots.length > 1){
				_getCell(roots[0]).addClass('tree-root-first');
			} else if (roots.length == 1){
				_getCell(roots[0]).addClass('tree-root-one');
			}
			_join(roots);
			_line(roots);
			function _join(nodes){
				$.map(nodes, function(node){
					if (node.children && node.children.length){
						_join(node.children);
					} else {
						var cell = _getCell(node);
						cell.find('.tree-icon').prev().addClass('tree-join');
					}
				});
				var cell = _getCell(nodes[nodes.length-1]);
				cell.addClass('tree-node-last');
				cell.find('.tree-join').removeClass('tree-join').addClass('tree-joinbottom');
			}
			function _line(nodes){
				$.map(nodes, function(node){
					if (node.children && node.children.length){
						_line(node.children);
					}
				});
				for(var i=0; i<nodes.length-1; i++){
					var node = nodes[i];
					var level = t.treegrid('getLevel', node[opts.idField]);
					var tr = opts.finder.getTr(target, node[opts.idField]);
					var cc = tr.next().find('tr.datagrid-row td[field="' + opts.treeField + '"] div.datagrid-cell');
					cc.find('span:eq('+(level-1)+')').addClass('tree-line');
				}
			}
			function _getCell(node){
				var tr = opts.finder.getTr(target, node[opts.idField]);
				var cell = tr.find('td[field="'+opts.treeField+'"] div.datagrid-cell');
				return cell;
			}
		})
	}
})
Usage example:
$('#tg').treegrid({lines:true}).treegrid('showLines');
I tried to extend the new method 'showLines' that you've mentioned above. But error occured!
TypeError: node is undefined[在此错误处中断]    
var tr = opts.finder.getTr(target, node[opts.idField]);
And I used js-create treegrid way, not html way. FYI:
$('#resourceTree').treegrid({
             url:'resource.do?method=getDynamicTreegridData',
             method: 'get',
             columns:[[
                 {field:'name', title:'name', width:190,editor:'text'}                 
             ]],
             lines:true,
             showHeader:false,
             onClickRow: onClickTreeRow,
             border:false,
             idField: 'id',
               treeField: 'name'
         });
$('#resourceTree').treegrid({lines: true}).treegrid('showLines');