Sorry, I was referring to the link Ashleyy gave you. It's a cool setup that I think someone did in the 4 gallon Finnex tank. It looks like they got some dried bamboo sticks and placed them in the tank like tree trunks. Then they floated wisteria (I think that's what plant they used) at the top of the tank to resemble tree tops.
If the tank isn't covered, you could add lucky bamboo to the tank. But you have to make sure the lucky bamboo leaves are exposed to the air (roots can be submerged in the water). Also, the water level in the tank would have to be kept lower than the top in case the betta wants to jump.
In the 6 gallon Edge, as long as you keep the water level down you could keep African Dwarf Frogs. But you have to be careful cause sometimes the betta doesn't want to live with them or eats their food. Some people have luck keeping them together. I would ask in the community tank thread and specify what tank you have and how many gallons. There are probably people more informed about it then I am.