Method and apparatus of syntax interleaving for separate coding tree in video coding

An apparatus of video encoding and decoding used by a video encoding system and video decoding system respectively, the apparatus comprising one or more electronic circuits or processors arrange to:

• receive input data associated with a current data unit in a current picture, wherein the input data associated with the current data unit comprise a luma component and a chroma component;
• partition the current data unit into multiple initial blocks using inferred splitting without split-syntax signalling when the current data unit is larger than M×N for the luma component, wherein each of the multiple initial blocks comprises an initial luma block and an initial chroma block, and wherein M and N are positive integers;
• determine a partition structure for partitioning the initial luma block and the initial chroma block of each initial block into one or more luma CUs (coding units) and one or more chroma CUs respectively;
• and
• signal or parse one or more luma syntaxes and one or more chroma syntaxes associated with one initial block in the current data unit and then signal or parse one or more luma syntaxes and one or more chroma syntaxes associated with one next initial block in the current data unit.