Posts.insert({
                    post:post,
                    author:username,
                    date:date,
                    createdAt:new Date(),
                    comment:{
                        commentBy:'',
                        commentMsg:''
                    },
                    userId:Meteor.userId()
                })

Posts.update(thisPost,{$addToSet:{comment.commentedBy:Name,comment.commentMsg:post}});