La mia conoscenza delle foglie d'acero è molto limitata. La mia comprensione è che le foglie cambiano dal verde ad altri colori quando la clorofilla non viene prodotta. Le foglie saranno quindi di un colore diverso a seconda del contenuto di zucchero. Questa spiegazione non ha senso quando si considera che l'albero è metà giallo e metà rosso. Non posso credere che il contenuto di zucchero nelle foglie sia proporzionato in modo diverso sui diversi lati dell'albero. Pensi che forse un lato è diventato dormiente più velocemente a causa dell'esposizione a nord e questo potrebbe spiegare un diverso contenuto di zucchero? Non credo, ma sono perplesso. Scusa.

Several explanations occur to me. I don’t actually know. But here is a go…

1. One side of the tree is exposed to somewhat different conditions to the other, such as prevailing winds, or cold. Perhaps it grows on a slope or a fold in the land where the bodies or air or the layers behave differently. It makes me think that the red night be induced by the cold, or it might be round the other way. One side of the tree might face east. If it gets morning sun, this means that side will warm up more quickly in the morning during the first chills of autumn, resulting in a different process by which the tree extracts nutrients back into the tree for the leaves and thus a different colour.
2. There is great variation in some maple species. For instance Silver maples can sometimes be quite red in the fall, whilst others can be clear yellow. In some plants a cell line can develop quite randomly in the plant in which pigments are different. This is called a “sport”. In roses this can be a different coloured flower (white instead of pink for instance) or variegation or golden foliage or bronze foliage instead of the usual green. It is possible that early in the tree’s life, it “threw a sport”, with the result that some branches turn red and other branches turn gold in the fall.
3. An outside chance is that there are in fact two maple trees growing right next to each other, so closely that they appear to be one tree, indeed could even have merged. Whether they are even the same species or two different ones will be best known to you. But it might be worth comparing and examining the leaf shapes of both sides in detail to see if there are any differences that are consistently different between the red and the yellow, which would help confirm the second possibility, and then close examination of the trunk, so see if there is any evidence of there being two trunks which have grown together.