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Professional edition supports smartParsing feature, which allow to work with tree of such size (in local sample it loads a tree with 50000 nodes), but the key point is a count of items per branch. If item has more than 100 child items then you can detect slowdown, and it really begins to work slow in case of more than 200 items per branch. So it all depends on tree structure. Well structured trees are loaded much faster than trees with big amount of items per branch.

Distributed Loading doesn't decrease loading time, it only allows to prevent browser freezing while loading big amount of items, and makes tree operable even not all items parsed from XML yet (it allows to decrease importance of well structuring )

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