Probably, yes, you should enclose that phrase in commas, but let's be sure.
If you enclose it in commas, then the meaning of the sentence is something like:
The maple tree stood in the entrance of the building and it was full of leaves.
The maple tree, which was full of leaves, stood in the entrance of the building.
This is probably the meaning you intend.
Without commas, the function of "full of leaves" is to specify which maple tree among many stood in the entrance of the building. This probably requires that you've already mentioned several trees, one of which was full of leaves, but you haven't mentioned where any of the trees were growing. To me, it is quite odd to describe a tree and its appearance without saying where the tree is to begin with. That's why I'm guessing this sentence doesn't follow your intent.