Adding a bundle increases build size

I want to make a build with only single one scene and almost no resources (it should be small in size) and a bundle with other resources to put it on remote.
I tried to change different settings. The very optimal way i found is to set ‘include in build’ to true, then build a bundle, then set ‘include in build’ to false, then build a build.
With small project itself it is hard to see a difference between options, cause my build weight is about 7.5mb and a bundle about 1.5mb. But when i put fot example 1.5mb texture to bundle the bundle size growth about 1.5mb and build growth about 1mb.
Idk why? Whe i put asset to bundle only bundle size should be changed, not build.