What is the difference between merging the trunk to a branch vs. a branch to the Trunk?

Question

I am relatively new to using the SVN for version control. I am trying to merge the recent development on my branch to Trunk.

For sake of this example, let us suppose that my branch is at revision r35357. The trunk is at revision r35486. The common ancestral point or the point from where the branch separated is r33285. I am trying the following two options to understand the merge process.

Option 1:- Merge Trunk to my branch

I use the following steps:-

svn co branch_url
cd above_checked_out_repository
svn merge trunk_url

Here is what I get:-

1. 4 text conflicts
2. 0 tree conflicts

I would also like to mention that I do this step quite often in my branch to keep my branch updated with the Trunk.

Option 2:- Merge my branch to the Trunk

I do the following steps in this case:-

svn co Trunk_url
cd above_checked_out_repository
svn merge branch_url

Here is what I get:-

1. 84 text conflicts
2. 500 tree conflicts

Can someone please explain why these two steps behave so differently? Why the deltas or the total difference between two options are so different?

I also tried the following:- After merging Trunk with my local copy (Option 1), I downloaded a fresh copy of Trunk and tried to compare the differences between the directory containing Trunk and my_current_branch using Meld. I got a few differences (approx 10) which is right because I added a couple of files and made changes in a few other?

Then, why the Option2 behaves so differently and has so many differences?

Also, what exactly is a tree conflict and how to resolve them? Can someone point to an appropriate resource?