There is a solution for both node-link tree or treemap. But it do require another tool since drawing this on Excel only would be very difficult if not impossible.

I propose to use the Funfun Excel Add-in which allows you to use JavaScript directly in Excel. With the capability of using JavaScript, you could make use the powerful libraries like D3.js or HighChart.js so that drawing tree chart would be much easier.

Here are two examples of generating trees in Excel.

I used D3.js in the first example and Hightchats.js in the second example. I made those two examples in Funfun online editor and then linked them to my Excel. You could check the code on the links below.

https://www.funfun.io/1/edit/5a36aaf145ac15144af3fe1e

https://www.funfun.io/1/edit/5925013604ce702ccfb22b0b

Here is what you need to do to link these samples to your Excel.

1). Insert the Funfun add-in from Office Add-ins store

2). Create a new Funfun or load a sample from Funfun online editor.

3) Have fun :)

Disclosure: I'm a developer of Funfun