This is possibly the world’s tallest in Crossville, Tenn
Modern tree houses are also typically quite eco-friendly. They have traditionally been built using salvaged materials, and now designers and builders have taken it further with energy-efficient features, such as composting toilets, or utilizing solar panels and fuel-cell power.
Read and see more tree houses at: http://realestate.yahoo.com/promo/amazing-treehouse-homes.html
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Green Real Estate Appraiser 
this is the best tree house i have ever seen in my entire life!!!!!!