I wanna make something like a "tree" or set of dropdown menus for my notes processor

So, I am making a notes processor. Currently, it can take a file from a folder of text files that the user chooses from via CLI, read over each line, save each line to a vector. What it can also do is see how many tabs are in front of a line. When I am writing notes I use tabs to indicate depth or specificity for a topic. I have each line and its "depth" value (tabs) stored in a array which is stored into a big vector. I wanna make like a tree with the root (a zero tab line), with branches for each line that is tabbed after that, how could I go about this?