I hope you can help me with this, as I've been questioning this since dream bubbles have been introduced, especially with Terezi`s and Aranea`s conversation in act 6 intermission 2. Aranea and Terezi are shown walking on a tree branch which is growing while they talk, which arises my question. Can the memories in dream bubbles be manipulated? Because I don't remember even a single tree Terezi`s land, which was where they were. Do you have the answer for this?

The memory wasn’t manipulated. They were just walking between memories.  The sequence you are talking about starts in Terezi’s hive, which is in a tree then gradually it changes to Terezi’s planet, then into the skies of Alternia.