If all you need is to adjust your derailleur, you can do it in a few ways without owning a stand:

• Look for a public bike repair station near you, where you can prop up your frame.
• Flip your bike upside-down. (Do it on grass or lay down some padding if you're worried about scratching your bike.)
• For your rear derailleur, shift to the second-smallest cog, squat behind your bike, close one eye, and sight it. You should be able to see whether the top of the chain, the cog, the derailleur, and the bottom of the chain are visually aligned. Tweak the barrel adjuster until it looks aligned and take it for a test ride.

But yeah, having a repair stand is useful. If you're looking for something super compact, there's the Altangle Hangar Connect, which turns any fencepost into a bike stand (but it's not cheap). The Topeak Transformer RX floor pump can kind of function as a stand in limited circumstances.

rope and tree branch?

If you are in the US, check any Aldis near you. No joke, got a quality stand for like $40, and it collapses down to fit in a corner or closet.

I'm using a Park Tool. It's good but it wasn't cheap.