King crimson maple
Hello and thanks for using Ask a Master Gardener with your question.
The item in question appears to be hatched insect eggs. When viewed up close, the tops of the eggs are missing, so that means the insect has hatched. What you are seeing would require no additional treatment, as they are empty and can do no harm to the tree. At this date, the leaves of the tree have produced most of the energy for the tree and will soon begin to drop from the tree. Unless the tree is young or only have a few leaves, you should observe minimal issues.
There are two options for the insect. One is the Brown Marmorated Stinkbug. They generally lay eggs in clusters of 28, which is what I count in your photo. They are a major pest of fruit and vegetables.
They have become a pest of the house. It is best to try and keep them out of your house by closing up all possible entry points such as small holes around the outside of the house. They should do minimal damage to your Maple tree.
Here are a fact sheet from Rutgers and a powerpoint presentation from an OSU professor about the insect and control:
The second insect that the eggs could belong to is a moth. The resulting caterpillars would be eating the leaves of your tree. Unless, again, the tree is young or has few leaves, generally there should be minimal damage to the tree. Look up the tree for caterpillars and I could possibly help identify them if you found any and sent a photo.
Again, the eggs appear to have hatched and I see no evidence of feeding, which would be the first thing new caterpillars would do. That leads me to believe it is the stinkbug.
Let me know if you need further identification based on something other than the hatched eggs. You should not need to treat the tree unless you have a huge infestation, then I need to identify to make a chemical recommendation.
Thanks for your question.