Why do my dwarves climb trees?

My base started on a mountain. I dismantled the wagon and made a large meeting area on two cliffs below. However it seems like that my units like to climb trees. In fact, one of my miners was found stuck in a tree rather than digging but eventually went down. I've searched dwarffortresswiki but only came across Adventure Mode. Is this a feature?

Climbing trees is meant to be a feature if your dwarfs can't get to their objective any other way. However, their aggressiveness in climbing up a tree and refusing to come down is a known bug. Often changing their labors around temporarily, or temporarily giving another dwarf the job they refuse to do, is enough to snap them back to reality. Sometimes they're stuck up there forever. This is DWARF FORTRESS!

Its a feature. On the wiki it says:

Trees can be climbed in both fortress and adventurer mode. In densely wooded areas, the overlapping tree crowns can form a continuous canopy that can be traversed by walking, climbing and/or jumping. Both types of branches provide floor-like support for walking, but twigs are too frail to support the weight of a dwarf. All kinds of trunk tiles are treated as solid barriers, except trunk tips - they can be walked and jumped over.

I couldn't find any source where this is concerned as an issue so its not really a problem.

In adventurer mode you can climb them yourself by pressing H to first hold on it and then moving by pressing the movement keys, but I guess you already figured out.

"tree" on dwarf fortress wiki

I think this is a feature and DF treats leaves and branches as normal pathable area. Nothing extraordinary or harmful about it, or at least I haven't encountered a case that would hurt (me).

It makes for funny situations in combat - I once had a squad of dorfs chasing a wereelephant through several trees, until it got too tired and slowed down.