The Treebeard constructor/intializer function, runTB is a bit unintuitive because it doesn't really return a new Treebeard instance; intstead, it returns a mithril module: https://github.com/caneruguz/treebeard/blob/93ff6df2f4e230db33736eb1850de4e471daa5db/scripts/grid.js#L2406
This leads to a number of "gotchas":
var treebeard = new Treebeard({...});
console.log(treebeard.options); // ERROR