nextVisibleNode() {
        let next;

        // 1. Any visible children
        next = this.nextVisibleChildNode();

        // 2. Any Siblings
        if (!next) {
            next = this.nextVisibleSiblingNode();
        }

        // 3. Find sibling of ancestor(s)
        if (!next) {
            next = this.nextVisibleAncestralSiblingNode();
        }

        return next;
    }
Get the next visible node.

@return {TreeNode} Node object if any.