There are much more vigorous roses for climbing trees, like mermaid or lady banks.  Don Juan is not a very rampant climber.  I do have a Don Juan growing through a Little Gem Magnolia.  It has threaded it's way up & over the top of the tree where it blooms in full sun, 15' apx.   There is an occasional branch that blooms from the midst of the magnolia.   The bloom stems are erect & can best be seen from above, in this case from the roof of the house, where I seldom find myself.   I have another Don Juan that is climbing along side a staircase to a high porch where it is much more easily enjoyed.