Question on headings numbering

[skaertus]

I am new to this forum, and this is my first post. I am not sure someone else posted a similar question, but I could not find anything related to this so far, so here it goes.



I am writing a book on MS Word, and I want a specific division of chapters. I would like the chapters to look like this, and I want my table of contents to reflect it:

PART I

1. Chapter 1
1.1. Sub-chapter 1.1
1.2. Sub-chapter 1.2

2. Chapter 2
2.1. Sub-chapter 2.1
2.2. Sub-chapter 2.2

PART II

3. Chapter 3
3.1. Sub-chapter 3.1
3.2. Sub-chapter 3.2

4. Chapter 4
4.1 Sub-chapter 4.1
4.2. Sub-chapter 4.2

However, I can only manage to have this:

1. PART I

1.1. Chapter 1
1.1.1. Sub-chapter 1.1
1.1.2. Sub-chapter 1.2

1.2. Chapter 2
1.2.1. Sub-chapter 2.1
1.2.2. Sub-chapter 2.2

2. PART II

2.1. Chapter 3
2.1.1. Sub-chapter 3.1
2.1.2. Sub-chapter 3.2

2.2. Chapter 4
2.2.1 Sub-chapter 4.1
2.2.2. Sub-chapter 4.2

How can I have headings reflecting what I want, with each "Chapter" being subordinated to each "PART", but with independent numbering?

Thanks for the help.