Even though they are leery of being taken advantage of, Leo prefers to be the person leaned on than to have to lean on or depend on somebody else.
It is quite uncommon for lions to climb trees due to their large size and mass, however this unusual phenomena has been known to occur. There are different explanations for these types of behaviors. Some speculate that lions may climb trees to escape biting flies and insects that are more prevalent at ground level or that lions may find that situating themselves at a higher level, they’d experience a more cooler temperature.
Although it is not common to see lions up in trees, its more usual to see younger lions and cubs sitting/climbing on trees rather than adults - due to their size and mass, its more difficult.
Its not certain whether this behavior is learned or innate (for example, hunting is innate, while stalking techniques are learned through watching their parents). Some prides have been observed to learn specific behaviors that benefit them, such as attacking porcupines in pairs - one in the front, one in the back. Depending on environmental factors and necessities, their behavior could change to accommodate. (source)