ArtMetal

So I'm getting married to a Godlike man, but the date is not yet set. Should save us some stress and money having to plan ahead, but there seems to be a bit of difficulty. We planned out wedding theme to be based off of A Song of Ice and Fire book series by George R. R. Martin. Which means we will need a large heart tree for our vows instead of an arch or such. Great. Where did I happen to have the brilliant idea to build a ten to twelve foot tree out of a foam material instead of just changing plans? No idea, but I am sadly excited about the undertakiing of a large project. :3 But I am already stick at materials and designing the freakin' tree. So now I'm stuck up a tree looking for lightweight designs and building materials, but I don't think styrofoam will work. Suggestions, anyone?