add more than one node to tree grid

data : array of data rows to be added 
data[n] should have id,parent,expanded,isleaf and loaded properties (loaded should be set to true)
example: 
data = [{coulmn1:"data1",id:"id1",parent:"null",expanded:true,loaded:true,isLeaf:false},{coulmn1:"data2",id:"id2",parent:"id1",expanded:true,loaded:true,isLeaf:true}];