Remove repeated occurences in column 2 - awk

Question

I have the following input file with 2 fields separated by tab. I hope to explain good enough.
Description
The field 2 contains chapters. In this case there are 2, HISTORY OF THE COUNTRY and PHYSICAL GEOGRAPHY,
All chapters are related with value 10 in field 1.
The sections beneath each chapter are related with value 07.
The content is related with value 05
The next chapter begins when $1==10 and $2 different than previous chapter.
In this case Chapter 1 goes from line 1 to line 16
In this case Chapter 2 goes from line 17 to end of file.
The chapters, sections and content could appear repeated times in field 2.
For example:
HISTORY OF THE COUNTRY appears 4 times between line 1 and line 16
PHYSICAL GEOGRAPHY appears 2 times between line 17 and end of file
My goal is:
Remove repeated occurrences of Chapters and Sections leaving all in the same order of appearence. For the content, don´t remove anything. I mean,
for chapter 1, remove repeated HISTORY OF THE COUNTRY within
chapter 1's context (between line 1 and 16)
for chapter 2, remove repeated PHYSICAL GEOGRAPHY within chapter 2's context (between
line 17 and 25)
The Input is this:
10 HISTORY OF THE COUNTRY
07 FIRST PART
07 INTRODUCTION
05 Article 1
10 HISTORY OF THE COUNTRY
07 FIRST PART
07 INTRODUCTION
05 Article 2
10 HISTORY OF THE COUNTRY
07 SECOND PART
07 REVIEW
05 Article 1
10 HISTORY OF THE COUNTRY
07 SECOND PART
07 METHODOLOGY
05 Article1
10 PHYSICAL GEOGRAPHY
07 FIRST PART
07 INTRODUCTION
05 First section
10 PHYSICAL GEOGRAPHY
07 FIRST PART
07 INTRODUCTION
05 Second Section
and output would be like this:
10 HISTORY OF THE COUNTRY
07 FIRST PART
07 INTRODUCTION
05 Article 1
05 Article 2
07 SECOND PART
07 REVIEW
05 Article 1
07 METHODOLOGY
05 Article1
10 PHYSICAL GEOGRAPHY
07 FIRST PART
07 INTRODUCTION
05 First section
05 Second Section
My current code prints something close, but not what I'm looking for.
awk '$2 in a {next} {
a[$2]++
}1' input.txt
10 HISTORY OF THE COUNTRY
07 FIRST PART
07 INTRODUCTION
05 Article 1
07 SECOND PART
07 REVIEW
07 METHODOLOGY
05 Article1
10 PHYSICAL GEOGRAPHY
05 First section
05 Second Section
To ease understanding, I show below the input with chapters in yellow and orange, sections in green. Besides that I show current output and desired output. Thanks for any help.

Answer 1

You may use this awk:
awk -F '\t' '$1 == 10 { ch = $2; sec = "" } $1+0 == 7 { sec = $2 }
($1+0 == 5 && !seen[ch,sec,$0]++) || !seen[ch,$0]++' file
10 HISTORY OF THE COUNTRY
07 FIRST PART
07 INTRODUCTION
05 Article 1
05 Article 2
07 SECOND PART
07 REVIEW
05 Article 1
07 METHODOLOGY
05 Article1
10 PHYSICAL GEOGRAPHY
07 FIRST PART
07 INTRODUCTION
05 First section
05 Second Section

Answer 2

another awk
You need to apply uniqueness in a path dependent way. Print all unique chapters, parts within a chapter, and articles/sections within a part.
$ awk '$1=="10" && !h1[c=$0]++;
$1=="07" && !h2[c,s=$0]++;
$1=="05" && !h3[c,s,$0]++' file
10 HISTORY OF THE COUNTRY
07 FIRST PART
07 INTRODUCTION
05 Article 1
05 Article 2
07 SECOND PART
07 REVIEW
05 Article 1
07 METHODOLOGY
05 Article1
10 PHYSICAL GEOGRAPHY
07 FIRST PART
07 INTRODUCTION
05 First section
05 Second Section
{print $0} is implied when the statement is missing.
in awk associated array a[k] (similar to hash maps) using the key k, initially equal to 0 or null value (false in boolean), post incremented a[k]++ and negated !a[k]++. So it will only be true for the first k, therefore can be used as a unique filter. Here h1, h2, and h3 correspond to unique headers at each level, where keys include the parent path as well, will only print the unique values based on the keys.
This script can be shortened for this problem but as given it's easy to modify if you need to add another layer.