tree.js

var Tree = function(value){
  this.value = value;
  this.children = [];
};

Tree.prototype.addChild = function(child){
  if (!child || !(child instanceof Tree)){
    child = new Tree(child);
  }

  if(!this.isDescendant(child)){
    this.children.push(child);
  }else {
    throw new Error("Already child");
  }
  return child;
};

Tree.prototype.isDescendant = function(child){
  if(this.children.indexOf(child) !== -1){
    return true;
  }else{
    for(var i = 0; i < this.children.length; i++){
      if(this.children[i].isDescendant(child)){
        return true;
      }
    }
    return false;
  }
};

Tree.prototype.removeChild = function(child){
  var index = this.children.indexOf(child);
  if(index !== -1){
    this.children.splice(index,1);
  }else{
    throw new Error("Not a child");
  }
};