guys i need way for add more than one instrumet to midi track
Welcome to the Ardour discourse.
First of all you, your question is not really clear. Perhaps you mean you want a multi-timbral synthesizer, one that will play e.g. piano on MIDI channel 1 and drums on MIDI channel 10. Or perhaps you literally mean you want to be able to add additional plugin instruments.
If the latter, just add a new instrument plugin, and when asked about “Replace or Add”, choose add.
Another way of doing Paul’s suggestion for multiple synths that play a single MIDI track, I personally find it more helpful to use MIDI busses for each instrument and route 1 MIDI track to multiple outputs. This makes it so each instrument/layer can be mixed individually.