Every year, thousands of people flocked to see unusual plants and innovative garden design (including bespoke tree houses) at The Chelsea Flower Show. This year’s exhibits included a garden that was co-designed by the Duchess of Cambridge. Teaming up with Davies White, the centrepiece of Kate Middleton’s design was an impressive treehouse. For this grand structure, the treehouse builders had erected a large oak platform onto the broad trunk of a chestnut tree. The platform was surrounded by an organic…