Tree the whales!

Let's start with the most basic of hierarchical charts -- a tree! Create a new function and fill it with the following:

westerosChart.tree = function Tree(_data) { 
  const data = getMajorHouses(_data); 
  const chart = this.container; 
  const stratify = d3.stratify() 
    .parentId(d => d.fatherLabel) 
    .id(d => d.itemLabel); 
  const root = stratify(data); 
  const layout = d3.tree() 
    .size([ 
      this.innerWidth, 
      this.innerHeight, 
    ]); 
}

We use our next-to-be-written getMajorHouses() function to filter out characters who don't have a fatherLabel property and whose itemLabel isn't set as anybody's fatherLabel property. We then create a new stratify object and set its parentId() accessor function to each item's fatherLabel and the id() accessor to each item's itemLabel. We're able to do the latter with this dataset because we know that each itemLabel is distinct; if this was not the case (for instance, if you had a dataset where there were a few...