javascript easyui treegrid点击行即可伸缩

treegrid点击小箭头才可伸缩，不方便；

    function drawtreegrid(data,id,filter,sort){        var col=[];        var arrdata=typeof data.rows!=='object' ? JSON.parse(data.rows):data.rows;        for(var index in arrdata[1]){            if(index!=='id' && index!=='_parentId'){            col.push({'field':index,'title':index,'width':100,'sortable':sort});            }        };        $('#'+id).treegrid({            data:data,            //singleSelect: true,            rownumbers: true,            //showFooter: false,            //fitColumns: true,            //remoteSort:false,            idField: 'id',            treeField: col[0]['field'],            columns:[col],            onClickCell:function(a,b){                if(a==col[0]['field']){                    if(b.state=='open'){                    $('#'+id).treegrid('collapse',b.id);                    }                    else {                    $('#'+id).treegrid('expand',b.id) ;                    }                }                else{                    return;                }                }        });          };