function insert(parentNode, dirs = []) {
    let dir = dirs.shift();
    // done, no more dirs to add
    if (dir == undefined) {
        return;
    }

    // exclude hidden directories
    if (dir[0] == ".") {
        return
    }

    let node = parentNode.get(dir);

    if (node == undefined) {
        // doesn't exist, add it
        node = new Map();
        parentNode.set(dir, node);
    }

    insert(node, dirs);
}
Recursively inserts directories into the Tree

@since 3.8.0

@param {map} parentNode current map instance representing a directory
in the password store fs Tree.
@param {array} dirs array of strings for remaining directories
     to be inserted in the Tree.