Cherry Blossoms Inin the Mountains

The period ofLast week, cherry blossoms ended up last weekfell in my city.

I am not sure what you are trying to say here

However, I could see thesaw a lot of cherry blossom trees while I was travelling.

In the high altitudes of the mountains, there have still beenare many wild cherry blossoms.

This sentence feels a bit out of place as you have already mentioned that you saw cherry blossom trees. To make it more natural, you could use present tense and say that there are cherry blossoms in the mountains generally.

In the middle of the green trees, there weare trees in white and pink trees.

Same with what I said above

Next year, I will climb up a mountain where there will havbe a lot of cherry blossom trees.

Cherry Blossoms Inin the Mountains

The period ofor cherry blossoms ended up last week in my cityin my city last week.

However, I could see thesaw a lot of cherry blossom trees while I was traveling.

In the high altitude mountains, there havare still been many wild cherry blossoms.

In the middle of the green trees, there were trees inalso white and pink trees.

Next year, I will climb up a mountain whereich will have a lot of cherry blossom trees.

"Next year, I will climb up a mountain where there will be a lot of cherry blossom trees." would also work.