jquery tree selection

I have cats with tree hierarchy, for example, country->city. So that you should first choose country, and then city. Or big catalog for products. You should choose several "folders", to get for specific product.

Yahoo's answers have this:

And some business ca开发者_JAVA百科talogs sites with big products lists.

I have all cats in php and can pass them to javascript.

How can I Implement it on one page? Is there any jquery plugin for this?

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We call this problem as cascading dropdowns problem. You can search on google as

cascading dropdowns using jQuery cascasding dropdowns Ajax

to get several examples.