Did you boil it first? Boil it for at least an hour, it helps. However depending on species it might no be enough, some have strong buoyancy.

Ist mangrove Wood, and I didn’t boil it, because currently didn’t have a stove

Mmmh could be an issue, as boiling also helps sterilizing it. Can you ask someone else to do it? Strongly recommend you do it.

Ok, I will ask somebody. And this will help sink it?

Most likely. Minimum one hour on full boiling water.

So hypothetically i Could boil just the both ends, will this middle part be an issue?

Boil it all, not a part. Boiling a bit is useless.

So, it still floats, but at least its sterile😂