Based on your description, I think you are trying to use load on demand so initially not all data is loaded in WebTreeView. If that so, we already provided a load on demand sample in the AdvancedLoadOnDemand.aspx and BasicLoadOnDemand.aspx

but the database is sql,how can i do??

please download the sql Code  below!

Give a c# Demo for  lazyLoading please! thank you!

Based on the screenshot you supplied, it seems you are using our WebGrid control, if you would like to create a treeview like structure from a single table, you could use the WebGrid self reference feature. The self reference feature also already support load on demand scenario as demonstrated in the sample SelfRef_LoadOnDemandChildRetrieval.aspx which available on the provided WebGrid sample.

the problen has been resolved !

but thank you all the same!