Unfortunately we do not have plans for implementing client side load mode for the RadTreeList. Indeed if the all items are loaded on the client and there is no need of postbacks for expand collapse. However what about the first load in this mode. If you have 10 000 items, the entire items hierarchy needs to be generated on the server, also all 10 000 will be rendered on the client and they need to be formatted, depending of each item level. All rows indentation needs to be calculated and all items need to be decorated based on that. So in this case you need to render html table with 10 000 styled rows, which could take several minutes and I think this is not acceptable too.
the Telerik team
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