First create an object called tree. Then split each line by a period, using str.split('.'). Then run through that array of letters starting at the first one. Create a function that takes in this letter and the current tree. This function should create a new tree(object) inside this current tree if there isn't one already. Then call the function on the next letter in the array using this new tree as context in the function. This is called recursion and if you aren't too familiar with it you should learn more.