It will be a great fun to take a lesson in History from you .
But before all, little English lesson. Please note the words “Indigenous” and “Indianic”( no such word in Dictionary though) are with different meaning. I used word“Indigenous”(phonetics: in·dig·e·nous) which has no link with India. This meansnative/local/Original. So please correct your understanding.
Now let us come to History. You told “We were even separate before being invade by India”. Please let us know the supporting resource for your claim. When Bengal was separated from India? Referring Stone Age? And when “India” invaded Bengal?
Globally accepted History (Non Madrassa off course) tells us the following facts-
1. In Mahabharata there is mention of few kingdom which are part of Bengal ( east + west) namely Anga ( kingdom of Karna), Vanga, Tamralipta etc. All of these Kingdoms participated in Kurukshetra war in favour Duryadhan. Many tells that Kurukshetra is a story of power struggle between East and West India. Earlier Jarasandh of Magadha( East India) was the most powerful King of India as per Mahabharata. After his death power centre shifted to West (Hastinapur)
Reference : htp // en wikipedia org / wiki/ Vanga_Kingdom
2. Then we found reference of a Kingdom called “Gangaridai” in the old Greek references namely Ptolemy and Megasthenes.
“Gangaridai (Greek:ΓανγαρίδαιGangaridae ; Gônggarriddhi, meaning "Wealth of the Ganges" ; Sanskrit: Ganga Rashtra, meaning "Nation on the River Ganges") was an ancient state found around 300 BC where the Bengal region lies today (present-day Bangladesh and the West Bengal state in India). It was described by the Greek traveller Megasthenes in his work Indica."
Reference : Archaeological Geography of the Ganga Plain: The Lower and the Middle Ganga.
3. During Gupta era (320-550 AD), Bengal was a part of Gupta Kingdom. Many Gupta era rock/brass edicts/ scripture were found across Bengal to prove it. Just a month ago many Gupta era gold coins were discovered in west Bengal. By the way, Gupta’s Capital was in Eastern India.
Reference : a. htp //en Wikipedia org / wiki / Gupta_Empire
b. htp //depts. washington edu / silkroad / exhibit / guptas / guptas.html
4. Around 600 AD, King Shashanka united whole Bengal. He expanded his Kingdom to Kamrup (Assam) in the east and also to part of North India. He defeated King Rajya Bardhana . The well known Chinese pilgrim/scholar /traveller Xuanzang (Hiuen Tsung)in his book mentioned a war between Shashanka and Harshavardhana. The scholar also visited Bengal during his travel in India.
“From Nalanda, Xuanzang travelled through several countries, including Pundranagara, to the capital of Pundravardhana, identified with modern Mahasthangarh, in Bangladesh. There Xuanzang found 20 monasteries with over 3,000 monks studying both the Hinayana and the Mahayana. One of them was the Vāśibhã Monastery (Po Shi Po), where he found over 700 Mahayana monks from all over East India , He also visited Somapura Mahavihara at Paharpur in the district of Naogaon, Bangladesh.”
Reference :
a. htp // en Wikipedia org / wiki / Xuanzang
b. htp //en Wikipedia org/ wiki/ Shashanka
5. Dharmapala ,the biggest Bengali emperor (Buddhist) ruled during (770–810 CE). He conquered almost all north India including present Pakistan.
“It is pointed out that Dharmapala had held a court in Kanauj after this victory which was attended by rulers from Bhoja(Berar), Matsya (Jaipur), Madra (Central Punjab), Kuru (Thaneswar), Yadu (Mathura & Dwaraka), Avanti(Malava), Yavana, Gandhara (Kabol valley = Kamboja) and Kira(Kangra). These chiefs not only approved of his military action but also paid respectful obeisance to him. It seems that Dharmapala had made himself the supreme leader in of Northern India since he calls himself as Uttarapathasvamin or Lord of Northern India.”
Reference : a. htp //en Wikipedia org /wiki/Dharmapala_(emperor)
b. htp //en wikipedia org /wiki/ Pala_Empire
5. During Muslim era also Bengal was one of the major part of India.
European traveller Bernier visited during Mughals wrote: "There is in Bengal such a quantity of cotton and silk, that the kingdom may be called the common storehouse for these two kinds of merchandise, not of Hindoustan or the Empire of the Great Mogol only, but of all the neighbouring kingdoms, and even of Europe."
Reference : htp // ww Columbia edu / itc / mealac/ Pritchett / 00islamlinks / ikram / part2_17 Html
The Last Nawab Siraj-ud-Daulah also used to rule Bengal and major parts of Bihar and Orissa
Therefore , from the above information and sources it is clear that since prehistoric era , Bengal was very much part and parcel of India which is on the contrary of your believe“Bd's history stop claiming like so that we're Indigenous . Even , people will laugh if you say so . Our history is a history of diversity , not of so called Indianic.”. Now I cannot blame people if they laugh at your sense of History.
This is the history what word recognised. So now please educate us with your version of Bengal/Bangladesh history with reference which you learned from your Madrassa and please show that it is independent of Indian History .
I believe Bangladesh became an independent country by virtue of itself. I always hope that the country will do very well in future. But for that there is no need to distort the history. Today’s Bengali/Bangladeshi carries cultural/religious heritage from Hinduism, Islam and Buddhism. You may annihilate Hidu/Buddhist part of your heritage but that will be your future not the history which cannot be changed.
Note :
As I am not allowed to post links yet, links given here are broken. Please add dots and remove gaps in between to get the actual links. I will be happy if somebody repost my post again with proper reference links
And Z.Iqbal ....well , if you wanna read a copy paste story read him . 
. There is nothing like this on the whole internet. 
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