adds a new item to the tree
obj | object | the item object |
index | number | optional, the position that the item will be added to (zero-based numbering) |
parentId | string | optional, the parent id |
string | ID of the newly added item |
//inserts a new item into the branch with id='root'
tree.data.add({id:"item10", value:"NewItem"}, 0, "root" );