I would suggest that your fictional planet might be less extreme than Venus yet still with total cloud cover and an uninhabitable surface.
In Poul Anderson's Orbit Unlimited Earth men colonized a planet of E Eridani (NOT Epsilon Eridani) with a thick atmosphere where only the highlands had air thin enough to breath.
In Larry Niven's known space stories Plateau, a planet of Tau Ceti, is Venus like and uninhabitable except on Mount Lookatthat, a California sized plateau rising up into breathable air levels.
It seems very illogical for the lower parts of plants to grow and survive in the conditions of the Venus surface and the upper parts of those same plants to grow and survive in conditions far above the surface where humans could survive. Those plant would seem to need to have different levels with totally different biochemistry on each level.
I could imagine plants like giant gasbags floating far above the surface, that send roots far down into thicker air to absorb nutrients, and send trunks and leaves high up above them to where the clouds are thin enough for the leaves to get enough light of the proper frequencies.
And on top of the trunks of those plants there could be parasite trees growing up higher and out above the cloud tops where your people could live. These trees would steal nutrients from the trees they grow on and their weight would keep the gasbags from floating too high and dying.
And possibly the deepest roots of the gasbag trees could get entangled with the tallest branches of other gasbag trees growing lower down with different biochemistry. Maybe there could be a chain of entwined gasbag trees with different biochemistries floating at different altitudes, going down to trees growing out of the surface. I don't know what the advantages of such a system would be.
Or one type of tree could grow from the tops of mountains where the conditions are not as bad as on the surface and parasitic trees could grow from their tops to pierce the clouds to Earth like conditions.
How tall can trees on Earth grow?
One answer is here: about 400 to 424 feet (122 to 130 meters).
It is true that there have been some reports of trees even taller than 400 to 424 feet, such as the legendary Ferguson Tree possibly reaching 500 feet or 150 meters. But many researchers scoff at reports of super tall trees.
And there is a newspaper report from 1927 of a petrified tree 896 feet long!
Another discussion of possible tree height is on this same site:
How tall can a tree grow?3
Some of the answers offer suggestions for solving the problems.
So even on a strange alien planet where conditions are different, it will be a little bit difficult for trees to grow tens of miles high to tower above the highest clouds.