From javascript how to fill RadComboBox Treeview control with json data

Work on vs2012 web form project.Want to fill RadComboBox  treeview control  by json data. To fill the control I use bellow
C# syntax. 

DataSet ds =dwdb.ExecuteDataSet("sp_getItemGroupsList");
ItemGroups iG =new ItemGroups();        
//find the
treeview  RadTreeView tree =(RadTreeView)this.RadComboBox1.Items[0].FindControl("RadTreeView1");
tree.DataSource = ds;        
tree.DataBind();


Need syntax how to fill RadComboBox by json data on client site.