ExampleMenu.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

using Nothke.SimpleMenu;
using TMPro;

public class ExampleMenu : Menu
{
    int intTest = 10;

    protected override void Create()
    {
        // A simple option with confirm
        root.Add(new Option("Confirm Example")
        {
            OnConfirmed = () => Debug.Log("Confirmed!")
        });

        // An option that changes when left or right is pressed
        root.Add(new Option() // We don't need a label since we'll override it in OnRevealed
        {
            OnValueChanged = (o, i) => intTest += i,
            OnRevealed = (o) => o.label = "Int: " + intTest,
        });

        // Adds a submenu with 2 options
        root.Add(new Option("Submenu")
        {
            options = new List<Option>()
            {
                new Option("Suboption 1") { OnConfirmed = () => Debug.Log("Foo!") },
                new Option("Suboption 2") { OnConfirmed = () => Debug.Log("Bar!") },
            },
        });

        root.Add(new Option("Quit")
        {
            OnConfirmed = () => Application.Quit()
        });
    }

    protected override void PlaceTextOnCreation(TMP_Text text, int index)
    {
        text.rectTransform.anchoredPosition = Vector2.down * index * 50;
    }
}

SimpleMenu.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using System;

using TMPro;

namespace Nothke.SimpleMenu
{
    public enum OptionType { Confirm, Submenu, Suboptions };

    public class Option
    {
        public string label;
        public List<Option> options;

        public Option parent;
        public int index;

        public Action OnConfirmed;
        public Action OnSelected;
        public Action OnDeselected;
        public Action<Option> OnRevealed;
        public Action<Option, int> OnValueChanged;

        public int Count => options == null ? 0 : options.Count;
        public bool IsSubmenu => options != null;

        public Option() { }

        public Option(string title)
        {
            this.label = title;
        }

        public void Add(Option option)
        {
            if (options == null)
                options = new List<Option>();

            option.parent = this;
            options.Add(option);
        }

        public void SelectChild(int i)
        {
            index = i % Count;

            if (index < 0)
                index = Count - 1;

            options[index].Select();
        }

        public void Deselect()
        {
            if (OnDeselected != null)
                OnDeselected();
        }

        public void ChangeValue(int by)
        {
            if (OnValueChanged != null)
                OnValueChanged(this, by);
        }

        public void Select()
        {
            if (OnDeselected != null)
                OnDeselected();
        }

        public void Reveal()
        {
            if (OnRevealed != null)
                OnRevealed(this);
        }

        public void ConfirmChild()
        {
            if (options[index].OnConfirmed != null)
                options[index].OnConfirmed();
        }
    }

    public abstract class Menu : MonoBehaviour
    {
        public RectTransform rootTransform;
        public TMP_Text textPrefab;

        public Option root;
        Option current;

        [NonSerialized] public List<TMP_Text> texts;

        private void Start()
        {
            root = new Option("") { options = new List<Option>() };

            current = root;

            Create();

            GenerateUI();

            Repaint();
        }

        protected virtual void GenerateUI()
        {
            texts = new List<TMP_Text>();

            for (int i = 0; i < 10; i++)
            {
                var tGO = Instantiate(textPrefab.gameObject);
                tGO.transform.SetParent(rootTransform);

                var t = tGO.GetComponent<TMP_Text>();

                PlaceTextOnCreation(t, i);

                texts.Add(t);
                tGO.SetActive(false);
            }
        }

        protected virtual void PlaceTextOnCreation(TMP_Text text, int index)
        {
            var pos = text.rectTransform.anchoredPosition;
            pos.y = -50 * index;
            text.rectTransform.anchoredPosition = pos;
        }

        protected abstract void Create();

        public void ReturnToRoot()
        {
            current = root;
            Repaint();
        }

        public void Show()
        {
            rootTransform.gameObject.SetActive(true);
        }

        public void Hide()
        {
            rootTransform.gameObject.SetActive(false);
        }

        public virtual void Repaint()
        {
            for (int i = texts.Count - 1; i >= 0; i--)
            {
                OnTextDeselected(texts[i]);
                texts[i].gameObject.SetActive(false);
            }

            int len = current.Count;
            for (int i = 0; i < len; i++)
            {
                texts[i].gameObject.SetActive(true);
                current.options[i].Reveal();
                texts[i].text = current.options[i].label;

                if (i == current.index)
                    OnTextSelected(texts[i]);
            }
        }


        private void Update()
        {
            GetInput(
                out bool down, out bool up,
                out bool left, out bool right,
                out bool confirm, out bool cancel);

            if (down)
                current.SelectChild(current.index + 1);
            else if (up)
                current.SelectChild(current.index - 1);

            var suboption = current.options[current.index];

            if (left || right)
            {
                suboption.ChangeValue(right ? 1 : -1);
            }

            if (confirm)
            {
                current.ConfirmChild();

                if (suboption.options != null)
                    current = suboption;

                Repaint();
            }

            if (cancel)
            {
                if (current.parent != null)
                    current = current.parent;
            }

            if (down || up || left || right || confirm || cancel)
                Repaint();
        }

        protected virtual void GetInput(
            out bool down, out bool up,
            out bool left, out bool right,
            out bool confirm, out bool cancel)
        {
            left = Input.GetKeyDown(KeyCode.A);
            right = Input.GetKeyDown(KeyCode.D);
            down = Input.GetKeyDown(KeyCode.S);
            up = Input.GetKeyDown(KeyCode.W);

            confirm = Input.GetKeyDown(KeyCode.Space) || Input.GetKeyDown(KeyCode.Return) || Input.GetKeyDown(KeyCode.KeypadEnter);
            cancel = Input.GetKeyDown(KeyCode.Escape) || Input.GetKeyDown(KeyCode.Backspace);
        }

        public virtual void OnTextSelected(TMP_Text text)
        {
            text.transform.localScale = Vector3.one * 1.2f;
            text.color = Color.yellow;
        }

        public virtual void OnTextDeselected(TMP_Text text)
        {
            text.transform.localScale = Vector3.one;
            text.color = Color.white;
        }
    }
}