>>531779125
>>531781730
Normal wood trees can be planted directly next to each other, but only 1 tree can mature within the 3x3 area, so for optimal wood tree placement you'd want now I've depicted it here.
The nice thing about wood trees is that they can grow even is there is debris or flooring around the tree. Wood trees do not grow during winter, unless you use a tree fertilizer on it.

Fruit trees however are super picky. They selfishly require full 9 squares and they are not allowed to overlap like with wood trees. Luckily the game prevents you from planting the fruits too close to each other, so you don't waste the sampling. Additionally, the 3x3 area must stay clear of all trash, debris and flooring during growth, so be sure to check behind the tree to see if there are any suddenly spawned grass or wood tree saplings.
Once fruit tree is mature and bearing fruit, then you can decorate around it with flooring tiles and other things.
Fruit trees do grow in any season, including winter, but they only bear fruit during their specific season. So you could plant cherry and apricot trees during winter and the trees would produce fruit in spring as they grow in snow.