Taxing the super-rich has been tried overseas and hasn't always worked out, one expert says. 

The Greens have set their wealth tax rate at 2.5%, but Treasury modelling suggests it could shrink the taxable wealth base by more than 40%.  

The party's own modelling puts the reduction at about 28%.  

Dentons tax partner Bruce Bernacchi told Kerre Woodham if introduced, we'd be only one of five countries that have it. 

He says in 1990 there were 12 countries in the OECD that had a wealth tax, and there are just four today. 

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